(apologies in advance for the lack of diacritics, I am home, ill, with no access to a unicode keyboard)

Purva Mimamsa authors are generally not interested in the topic, whereas several Uttara Mimamsa (i.e. Vedanta) ones deal at length with the status of the Mimamsasastra (I am tempted to say that, similarly, Christians alone are concerned with the unity of the two testaments within the Bible).
A particularly puzzling element, in this connection, is the status of an “intermediate part” of the Mimamsasastra, variously called madhyamakanda (as opposed to the karma– and brahmakandas or to the purva– and uttara– ones, i.e., the Purva Mimamsa Sutras, henceforth PMS and the Vedanta Sutras, henceforth UMS), or Sankarsa(na)kanda, but also devatakanda or upasanakanda. Neither of these names is found together with any other one, so that it seems clear that the basic assumption for the Mimamsa (both of Purva and Uttara Mimamsa) authors interested in the topics was that there were (at most) three basic texts of the Mimamsa Sastra.
Now, the problem is that the extant Sankarsa Kanda (henceforth SK), preserved in a few manuscripts and edited together with a commentary by Devasvamin or with a later one by Bhaskararaya, is a rather boring text, dealing with technicalities of the ritual. I would locate it in the Srauta-Sutra–Purva Mimamsa milieu, in the sense that it deals with technical details and does not seem to me to aim at more general problems. Thus, it makes good sense that Sabara twice refers to it (see this post) or that Somesvara does it once, but that no more Purva Mimamsa energies are dedicated to it. I might be wrong, but I am reminded of the complements to Panini’s Astadhyayi, such as the Dhatupatha, in the sense that Sabara seems to refer to the SK as to an appendix of the PMS, which does not need a specific exegetical attention (and, in fact, he did not comment on it).

A further significant detail is that the content of this SK does not correspond neither to the appellation devatakanda, nor to the function ascribed to it by Venkatanatha/Vedanta Desika and by other Vedantins, i.e., the discussions of deities, later to be subsumed within the brahman in the UMS.

By contrast, the SK–Devatakanda referred to by such Vedantins as Vedanta Desika in his Sesvara Mimamsa fits nicely in a progressive scheme: the PMS deals in this interpretation with karman, the SK with deities and the UMS with brahman.
Which sutras are attributed to the one or the other? Sabara (two sutras), Somesvara and Sankara (one sutra, see below) mention sutras also found in the extant SK, whereas later Vedantins either do not quote anything at all or quote a) the sutra quoted by Sankara (so Ramanuja, SriBhasya ad 3.3.43), b) the same three (or four) theistic sutras referring to Visnu and not found in the extant SK (so Venkatanatha in his Satadusani and in the Tattvatika, and Madhva in the Anuvyakhyana).
I counted three to four sutras because Madhva’s Anuvyakhyana mentions three (athato daivi (scil. jijnasa?), ya visnur aha iti and tam brahmety acaksate), which should occur, respectively, at the very beginning and at the very end of the SK. Venkatanatha does not mention the first one, but has the last two preceded by ante harau taddarsanat. tam brahmety acaksate makes indeed a smooth transition to the UMS. Jayatirtha’s commentary to Madhva attributes them to a Devasastra, an appellation which could refer to the SK-devatakanda previous to its confusion with the SK (see below).
Further four slokas from some sankarsanasutresu and not present in the extant SK are found within Utpala Vaisnava’s commentary on the Spandapradipika.

A further significant element is the connection with the Pancaratra. Already Sankara mentions the SK in his UMS-Bhasya in the context of a sutra (3.3.43) which is interpreted as discussing the validity of the vyuha doctrine of the Pancaratra. Further, Kanazawa mentions a very interesting passage by Mukunda Jha Bkashi, the editor of Raghavabhatta’s Padarthadarsa (15th c.), who writes that the PMS refer to the Brahmanas, the SK to the Pancaratras and the UMS to the Upanisads, thus distinguishing them on the basis of their referring to a different part of the Veda. In the passage the editor comments upon, Raghavabhatta attributes the upasanakanda to Narada and the UMS to Vyasa (who is regularly identified with Badarayana, see, e.g., Venkatanatha’s Satadusani 3). Who is this Narada? In any case, the name is connected with the Vaisnava milieu and it figures together with Sankarsana in the guruparampara leading to Vyasa in the (Vaisava) Hayagrivopanisad (Kanazawa, p. 41).
And the connection with the Vaisnava (and perhaps Kasmirian) milieu and, thus, with the Pancaratra is reinforced by Utpala Vaisnava’s quote.

To sum up, the extant SK does not seem to properly fulfill the role assigned to it by Vedantin authors.
A possible explanation could be that Vedantin authors used the name of a text which was assumed as part of the unitary Mimamsa Sastra but was either lost or little known (remind the lack of quotations of the extant SK in Vedanta Desika) and confused it with a different text which fulfilled a role which they needed to see fulfilled, i.e., that of introducing God in the Mimamsa system. Perhaps Kanazawa is right in pointing out that the very name SK might have helped, due to the importance of Sankarsana in the Pancaratra vyuha doctrine (Kanazawa, p. 40).

It is still difficult to tell how and when exactly did this superimposition of the one text on the other take place, but, as already hinted at, it seems to have taken place in Vedanta-Pancaratra milieus and Sankara may have played a major role in it, since he quotes from the extant SK, but in the context of a theological-Pancaratrika discussion. It might, thus, have been Sankara (or his Pancaratra opponent) who made the SK’s role shift from sheer technical discussions to theological ones. In other words, previous to Sankara there might have been a technical SK and a theistic text (perhaps only a few sentences). If we accept Jayatirtha’s authority, the latter had already a Vedantic flavour and we might speculate that it had been used by Vaisnavas (perhaps: Pancaratrins) who wanted to vindicate the Vedanta status of their system. Sankara’s quote of the former SK in a context where one could have expected the latter may have created the confusion between the two, a confusion which was very much welcomed for non-Advaita Vedantins and which harmonises nicely with further tripartitions (e.g., the one between karman, jnana and bhakti).

A further scenario would require one to assume that no SK-devatakanda ever existed and that some Vedantins artfully manipulated the evidences regarding the SK, but since attestations regarding it range well beyond the borders of an interconnected group of people, this scenario is at the moment less likely.

Last, it is possible that there existed a tradition of interpreting the extant SK in a theistic way and that it was in this connection that some further theistic sUtras have been attributed to it. Although this hypothesis clashes with the fact that no sutras of the extant SK have been transmitted together with the SK-devatakanda ones, it is probably right in pointing out that the confusion was quite ancient. Anandagiri’s explanation of the name sankarsa, for instance, refers to the technical contents of the extant SK, but then calls it devatakanda (sankarsyate karmakandastham evavasistam karma samksipyocyate iti sankarso devatakandam).

The Purva Mimamsa milieus seemingly remained unaffected by this move (remind Somesvara’s quote from the extant SK as late as in the 12th c. and the general lack of interest for the SK).

Which scenario seems to you more plausible?

On the SK, see this post and this one