Uttamur T. Vīrarāghavācārya discusses the reasons for having to deal with epistemology while trying to understand dharma in the context of PMS 1.1.3: We need to deal with epistemology because there are too many disagreements about what dharma is and how to know it. Here he summarises the Lokāyata position:

The position of the Lokāyatas is [as follows]. In ordinary experience (loka), there should not be distinction between what follows the rules (nyāyya) and what does not, or not (there should be a distinction)*.
The [condition for knowing] about dharma, adharma, etc. does not exist at all.
Since it (dharma) is understood in each time different ways by the upholders of the various opinions (mata), only its absence is apprehended.
Therefore, the condition of what should be investigated?

like nyāyyānyāyyavibhāgo mā bhūt, mā vā. dharmādharmādikaṃ nāsty eva. tattanmatasthair anyathānyathā tadabhyupagamāc ca tadabhāva eva pratīyate. ataḥ kasya niṃmittaṃ parīkṣyam iti lokāyatamatasthitiḥ.

*I am puzzled by the mā vā. If this reading of the subcommentary by Uttamur T. Vīrarāghavācārya is correct, the Lokāyata position is described as altogether sceptical. They do not even maintain that there can be no distinction between nyāyya and anyāyya. How would you interpret the mā vā?

Vīrarāghavācārya was a 20th c. Viśiṣṭādvaita Vedāntin whose editorial and commentarial contribution to his school will remain impressive for many generations to come. Personally, I am particularly pleased by his attempts to think along the tradition in a creative way.

Within his subcommentary on Vedānta Deśika’s Seśvaramīmāṃsā, Vīrarāghavācārya is at times closer to Viśiṣṭādvaita Vedānta than Vedānta Deśika’s pro-Mīmāṃsā attitudes. At other times, he just elaborates further on Vedānta Deśika’s hints. In one of such cases, he describes how the choice of words in Pūrva Mīmāṃsā Sūtra 1.1.2 (codanālakṣaṇo ‘rtho dharmaḥ ‘Dharma is that goal which is known through Vedic injunctions’) was not at all casual. Rather, each word had a direct meaning and also further suggested something more. For instance, codanālakṣaṇa is not just the same as codanāpramāṇa, but rather suggests that the Vedic injunction also defines what dharma is. dharma is also to be interpreted etymologically as ‘instrument of dhṛti‘, where dhṛti means prīti ‘happiness’. Similarly, artha indicates that bhakti is the result to be achieved, consisting in pleasing God. Then he sums up:

Through the word dharma, which means instrument for dhṛti, Jaimini also suggests that this ritual action devoid of desire which is a purpose in itself (svayamprayojana) is different than the instruments for the results consisting in the four human aims, which are expressed with reference to their own contents (svaviṣaya) [only]. [He suggests it] because through this [word dharma] also pleasing the Revered one (bhagavat) is communicated (uddeśya).

dharmapadena dhṛtisādhanavācinā caturvargaphalopāyāḥ ye svaviṣayāḥ vācyāḥ tais saha anlat svayaṃprayojanaṃ niṣkāmakarmāpy asūcayat bhagavatprītes tatroddeśyatvāt.

In other words, bhakti points beyond oneself, to God, whereas all other purposes remain confined to oneself.

The SM 1902 edition reads:

sphoṭas tvaṃ varṇasaṃghasthaḥ iti mahābhāratavacanam

The Mahābhārata statement “You are the sphoṭa, which is present in the conjunction of phonemes”.

Other manuscripts read varṇasthaḥ or varṇasamudāyaḥ instead of varṇasaṃghasthaḥ (both unmetrical). The Śatadūṣaṇī 30 reads sphoṭas tvaṃ varṇasaṃśraya iti mahābhārate ‘py ucyata iti cen na. The same quote is reused also in the Tattvamuktākalāpa with a different reading: sphoṭas tvaṃ varṇajuṣṭas tv iti yadabhihitaṃ bhārate sāpi śaktiḥ (v. 89, section 314).

Do readers know anything similar in the Mahābhārata? And who could be uttering it? Addressed to whom?

To my knowledge, Veṅkaṭanātha’s Seśvaramīmāṃsā (henceforth SM) has been commented upon only once in Sanskrit, namely in the 20th c. by Abhinava Deśika Vīrarāghavācārya.
Vīrarāghavācārya continues Veṅkaṭanātha’s agenda in reinterpreting Mīmāṃsā tenets in a Viśiṣṭādvaita Vedānta way.

On the meaning of dharma and on the polemics between a sādhya and siddha interpretation of the Veda, he writes:

Deities need to be pleased (ārādhya), what needs to be realised is the result.

(ārādhyā devatāḥ, sādhyaṃ phalam, ad SM ad PMS 1.1.1, 1971 edition of the SM, p.10)

Similarly, within the commentary on SM ad PMS 1.1.2, Vīrarāghavācārya interprets a quote by Parāśara Bhaṭṭa according to Maṇḍana’s distinction among various deontic concepts and then adds a further level:

The instruction which has necessarily to be performed is the command. The permission is the instruction which presupposes a desire for the experience of a result which is not forbidden. It has as content something desirable. An instruction having as content a forbidden purpose (as in the case of the Śyena) is a permission which has occurred automatically [but will be later subdued] (āpātānujñā).

The added level is labelled āpātānujñā. This is, as far as I know, a neologism. It indicates the fact that prescriptions about malefic sacrifices are not the Veda’s final words on the topic. They look like prescriptions, but in fact:

1. like all other textual passages presupposing human desires, they are only instructions about how to reach something, they do not state that one should desire it.
2. on top of that will then be sublated insofar as they presuppose a purpose which is prohibited in another part of the Veda.

Point 1 is a standard Mīmāṃsā devise to justify Vedic passages about malefic sacrifices. Vīrarāghavācārya adds point 2 to the landscape, thus highlighting that the textual passages about malefic sacrifices are ultimately sublated insofar as the purpose they presuppose is prohibited.

Vīrarāghavācārya probably formed the term āpātānujñā on the basis of āpātadhī. This is a term introduced by Rāmānuja and discussed at length by Veṅkaṭanātha. It means `automatic understanding’ of the Veda, the one one gathers while learning the Veda by heart without caring for investigating into its meaning. Such an automatic understanding will be later revised while one investigates the meaning of the Veda. Vīrarāghavācārya implicitly suggests that it can even be completely reversed.

Have readers ever encountered the term āpātānujñā?

At a certain point in the history of Mīmāṃsā (and, consequently, of Vedānta), the discussion of the reasons for undertaking the study of Mīmāṃsā becomes a primary topic of investigation. When did this exactly happen? The space dedicated to the topic increases gradually in the centuries, but Jaimini and Śabara don’t seem to be directly interested in it.

Nonetheless, Śabara needs to explain a related topic, namely when studying the Mīmāṃsā —before or after one’s study of the Veda. Kumārila and Prabhākara introduce the prescription to learn the Veda (svādhyāyo ‘dhyetavyaḥ, see Kataoka 2001b) and the one to teach the Veda, respectively, as the prescriptions prompting the study of the Veda and, indirectly, of its meaning. Kumārila explains that the prescription to study the Veda does not include a result which can be independently desired and that one therefore needs to insert the knowledge of its meaning as the result. Prabhākara explains that a teacher needs to know the meaning of the Veda in order to teach the Veda and that the dignity of being a teacher is something independently desirable.

The space to the topic of why studying Mīmāṃsā and which prescription promotes it increases drastically —I would say— after Śālikanātha (8th c.?). Why did this question become relevant? Perhaps because its answer was less obvious and one needed to persuade a different kind of public. A public who knew of the importance of studying the Veda, but was not immediately convinced of the importance of undertaking also a detailed study of the Mīmāṃsā exegesis. I wonder whether part of the problem is due to also to a) Śaṅkara’s statement that the Vedāntins do not need to study Mīmāṃsā and b) the fact that the Mīmāṃsā presents itself as a Vedic exegesis, but in fact looks at the Vedas from the vantage point of the Brāhmaṇas, so that an audience more interested in other parts of the Vedas might be less convinced of the usefulness of Mīmāṃsā.

Veṅkaṭanātha, though primarily a Viśiṣṭādvaita Vedāntin, dedicates the first 28 pages of his commentary on the Pūrva Mīmāṃsā Sūtra to this topic. He refutes both the Bhāṭṭa and the Prābhākara points of view. The Bhāṭṭas are wrong because the knowledge of the meaning of the Veda is not something independently desirable. The Prābhākaras are wrong because the prescription to teach is not sufficiently established and, even if it were, it would not include the knowledge of the meaning of the Veda.
Veṅkaṭanātha analyses at length all position and then concludes briskly that the study of Mīmāṃsā needs to be undertaken out of one’s desire (hence the desiderative ending in PMS 1.1.1). In order to legitimate this desire, Veṅkaṭanātha is able to show that PMS 1.1.1 (through the linguistic expression atha) shows that taking time to undertake the study of Mīmāṃsā does not violate other prescriptions and that there is a suitable time for it.

European readers may feel some sympathy with Mīmāṃsā authors, who were possibly just intellectually interested in Mīmāṃsā exegesis, but had to face external challenges and to structure their intuitions about the Mīmāṃsā being “interesting” into a consistent research project.

Śabara suggested that such seeming names in fact only express something else and offered alternative etymological explanations. Veṅkaṭanātha replies that out of context it is clear that specific people must be referred to, but that these people’s roles are recurrently covered at each new era.

The relevant passage by Śabara on PMS 1.1.31 reads:

[The name] ”Prāvāhaṇi” derives from `flowing forth’ (pravah-). [The name] ”Babara” imitates a sound. Therefore, these two [linguistic expressions] express only a permanent referent (artha). Therefore it is said \textbf{The other [ephemeral things mentioned in the Vedas], by contrast, are merely similar in the way they sound.

pravāhayati, sa prāvāhaṇiḥ. babara iti śabdānukṛtiḥ. tena yo nityārthas tam evaitau śabdau vadiṣyataḥ. ata uktam – paraṃ tu śrutisāmānyamātram iti

Veṅkaṭanātha’s rejection of this view reads as follows:

Only Half-Materialists (ardhacārvāka) like this construction (yojanā) [of the sūtra]. Otherwise, how could [such meanings] be connected (anvaya) with [linguistic expressions such as] ”he desired”? (How could ”Babara” be connected with ”he desired” if it is only an onomatopoeia?)

[Obj./in favour of Śabara:] Also in regard to that (”he desired”) one postulates a different meaning.

[R.:] Why should not [a different menaning] be postulated in this way in every case?

All four manuscripts of the Seśvaramīmāṃsā reproduce Śabara’s passage in a slightly different way, including a reference to vāyu as a referent of Prāvāhaṇi:

[The name] ”Prāvāhaṇi” derives from `flowing forth’ (pravah-). [The name] ”Babara” imitates a sound. Therefore, these two linguistic expressions express only a permanent referent (artha), [i.e.], the wind (which flows forth).

pravāhayati iti prāvāhaṇiḥ. babara iti śabdānukṛtiḥ. tena yo nityo ‘rthas tam imau śabdau vadiṣyataḥ vāyum. ata uktam – paraṃ tu śrutisāmānyamātram iti

The mention of vāyu is not present in the published version of the Śābarabhāṣya. Nonetheless, the reference to the wind is well-attested in the Mīmāṃsā subcommentaries on this adhikaraṇa, thus Veṅkaṭanātha could easily be aware of it.