We know that Pāḷi is a homogenisation of MIA dialects for ecclesiastical Theravāda purposes.
Except that there were no "MIA dialects" in Ashoka's era (or before) that Pali could have been a homogenization of. The supposed distinction between OIA and MIA was totally unknown until about half a millenium after the time of the Buddha. Pali is the ‘mother’ of the MIA dialects (i.e. MIA evolved from Pali), Pali is not a standardization of some pre-existing MIA dialects.
Pali standardized several written variations of the same OIA (not MIA) words. The Pali forms of words was an artificial standardization meant to reconcile these variations (most of which were errors caused by the use of defective scripts) and make them look consistent.
There is no independent evidence for the pre-existence of a single MIA spoken dialect that Pali could have standardized.
Besides a close reading of Pali word-forms in Ashoka's edicts (particuarly the OIA words having conjunct consonants) indicates that the places where such conjuncts occur was usually marked by a dot.
So "Dharma" was written as "dha.ma" in Brahmi (not as dham.a, please note). This was interpreted by some (particularly in the later Theravada tradition as dhamma) however I have valid reasons to believe that the dot represents a conjunct rather than a geminate. To understand the history of Pali therefore needs an understanding of its earliest script (Brahmi).
That Pāḷi as a language of the Theravāda canon represents a homogamy of MIA languages written during the reign of Aśoka e.g. the epigraphy of that period, does not tell us that Theravāda bhikkhus (or others on their behalf) used a written form of it for the preservation of the canon.
It does not matter. We are dealing with written texts all along, it is the oral tradition which we have no evidence of.
The Milindapanha mentions not just writing but hints at a written tradition, by naming certain eminent monks who were formerly skilled in that art... writing therefore was not only used by monks but was a prized skill. Why should buddhists in the BCE era have given such importance to writing if they had an independent oral tradition?
Are these with reference to non-Pāli Buddhist translations from MIA to Sanskrit during the reign of Aśoka? Please give some examples and how they are evidence of a written Pāḷi transmission.
Your question shows an ignorance of the fact that there was no (phonetic) Sanskrit writing in Ashoka's time, and therefore no possibility of a translation from or to Sanskrit -- all written Sanskrit was of the middle-Indic kind (i.e. non-phonetic). Besides I assume by Sanskrit you mean Old-Indic generally, rather than Panini's grammatical standard of Old-Indic (i.e. classical sanskrit). Do not mix them up, they are two very different things.
All the phonetic transliterations (they were not really translations) back into Old-Indic happened a century or more after Ashoka, by when the brahmi script had evolved into a fully phonetic script.
Yet the saṅgha was not just preserving a language, they were constructing a language derived from several dialects. They undoubtedly possessed the ability.
Nope, there is no evidence of them constructing a language. They were artificially standardizing the different word forms found in various written texts (the suttas were not an ordered part of the canon initially, they were independent suttas). For example, dharma was sometimes written as dhrama, sometimes as dhama, sometimes as dhamma, sometimes as dharama, etc.
This in any case does not show they possessed an ability to orally transmit a large corpus of prose texts down several generations.
Earlier you dismissed the comment I made with reference to catechetical instruction used in the Nikāyas.....This is evidence within the Nikāyas of at least the ability to an oral transmission
No, catechetical instruction is no evidence of the ability of photographically memorizing thousands and thousands of pages of prose and of their unerring literal oral transmission. I don't see the connection. We all have the ability of an oral transmission, but of what? We can and do orally transmit nursery rhymes, but we cannot orally transmit a 1000-page prose book. The ability of an oral tranmission in general therefore proves nothing.
In addition to the above request for references, can you cite any Buddhist manuscripts from this period, with reference to Pāḷi textual transmission?
That is another topic altogether, I do not want to venture into that topic here. Pali manuscripts from India are in such short supply because there is a widspread misconception about the Buddha's geographical region (the region in which he lived and travelled). Archaeologists have been digging in the wrong places.
The few manuscripts that we have of BCE era Buddhism are in pre-standardized Pali (called by some as Gandhari). http://www.gandhari.org
is a good online resource to look for information about them.
Again, is there any evidence you can cite or reference other than your opinion?
What kind of mnemonic system do you know of that the Buddha may have used?
Reference to the Milinda-pañha and Nāgasena is rather late, but even if this exchange was current at the First Council it does not transport writing into the hands of the saṅgha simply because of Nāgasena's simile.
There are more direct references to theravada scribes in the Milindapanha, like the one below:
“Long ago there was a master of writing named Tissa Thera. How can people know about him?”
“By his writing.”
So if the Milindapanha belongs to the 1st century BCE, then it refers to Tissa Thera as a master of writing long before that time.
Hypothetically, even if writing was done for them and the texts provided for their use, there is the matter of the above mentioned pācittiya on reciting to the laity.
No, there is no such pācittiya. There is one where it says a monk cannot chant with a layperson, but none that says a monk should not chant in front of (or to) a layperson.
These are all interesting opinions, but as you say, ‘archaeology might yet yield…’ something to back up your claim.
Archaeology has already yielded written BC era texts (both sutta and non sutta texts), visit the website I have mentioned above. What archaeology has not yielded yet is any evidence of an oral tradition.