Like most things when it comes to the suttas, this is more complex than it seems.
Sure, there are plenty of places where the abbreviation of a formula like the jhanas or the recollection of the triple gem is obvious, and expanding it would seem to be unproblematic.
But the process rapidly runs into snags. Consider, for example, the suttas of the first chapter of the Digha, where a very long passage requires expansion, and it is not always obvious how they vary from sutta to sutta. Ven Anandajoti is one of the few people to have tried to properly expand a heavily abbreviated text—the Satipatthana Vibhanga at Vb 7—and he said it was one of the the hardest things he’s ever done. You can read his detailed and excellent study on his website.
Even harder is the repetition series. If we fill all these out, what have we created? Certainly nothing like any manuscript that has ever existed. Nor, I am sure, have all these ever been actually recited. Can we say they existed in memory? Maybe. But really, they’re more like procedurally generated web pages, something like a search results page, which might in principle exist if someone searches for that exact string, but in fact no one has ever done so. These series are undoubtedly artificial, so what exactly is the purpose of expanding them?
Then consider the Chinese texts. Like all early Buddhist texts, they have lots of abbreviations. yet they handle them somewhat differently than the Pali. For example, they often have a short statement saying that the passage is to be expanded. If we expand them according to instructions, is the instruction still a part of the sutta, or not?
The expansions themselves are also not clear. In the Satipatthana Sutta, for example, the Chinese text usually has a short version of the satipatthana formula. But this is not an obviously truncated text, it reads perfectly well. You’d think it was just a variant of the Pali formula that happened to be used in that tradition. But half-way through the collection, the full formula appears, together with a note to the effect that all the suttas of the collection should be expanded in the same way. So the short version is an abbreviation, not simply a variant. Maybe we decide to expand them in that case. But the same short formula appears in other related texts outside the Satipatthana Samyutta. Are we to assume that the instructions for expanding the text apply there as well?
In other cases, we encounter “double-abbreviated” texts. A certain text is abbreviated, and instructs that you should expand according to another text; but that text too is abbreviated, and must be expanded following a third text.
Okay, so let’s say we can develop a markup system that categorizes all these various kinds of expansion. We work through 10,000,000 words of text in four ancient languages to apply the markup consistently. Goodbye weekends! Ha ha, only joking, monks don’t get weekends.
At the end of the day, we don’t have anything that resembles any traditional corpus. Nor is the process objective; it would require constant subjective decisions about what kind of markup applies and how the expansions are to be handled. But plain old marked up text is pretty useless. Next, we’d have to make use of it, for example, by developing a search engine that filters results according to the specified markup scheme.
Then there is, of course, the question of translations. For a translation, the abbreviations pose an entirely new kind of problem, that of readability. So no matter what scheme you developed to handle the original languages, you’d need a whole new scheme for the translations. But these are also not unified. You’d want separate versions, say, for print and web. Or for different translation styles.
And so it goes.
Practically speaking, I discussed this briefly with Ven Brahmali. We are both using a similar strategy in our translations. We try, so far as seems reasonable, to minimize repetitions within a particular text, but to expand passages if they require referring to another text.
In terms of detailed expansions of texts, for the forseeable future, this is something that will only really work in specialized studies like those of Ven Anandajoti.