However, a definition of svabhava from Nagarjuna would still be useful here, however. And likewise too for the Theravada definition. Although it isn't really in use in the Tipitaka, that is avoiding the issue. How is it defined in the para-canonical literature? This is why I ask about the "Theravada" rather than "Pali sutta" definition.
Yes, it would be useful to have some insight into exactly how these things were regarded and discussed. The quotes from Tiltbillings that I gave above suggest to me that modern dismissals of the Theravada literature tend to paint rather simplistic picture of the depth of the discussion that went on. It seems extremely unlikely that, either in ancient times or now, there were one or two scholars, such as Nagarjuna or Nanananda, who saw things clearly, and the rest were a bunch of deluded fools.
The progression of knowledge in any field simply doesn't work like that in any field I know anything about.
One thing I like to keep in mind, is that when a subsequent body of literature and thus thought appears, it does not at all mean that the previous body of literature and thought therefore vanishes, or that even a majority of people accept and uphold the newer body.
I fact, if we took modern fields of study as a reference point, one could probably argue that when a particular new idea first appears in print (as opposed to just being thought about), it may often meet with much resistance. The majority may well still hold to previous notions.
Moreover, the discrepancy between the thought of the specialists in the field, and that of the appearance in public, may entail quite some delay time wise. Appearance of texts only gives a terminus ad quem, rather than an actual starting point.
Relative profusion of literature may or may nor indicate popularity of the idea, either amongst scholars or the public at large. There may be some relationship, but fringe groups with massive publication efforts can slant things (like the Scientology people buying all their own books!) And this is also only at that time. What remains for later will have other factors. Paleographical evidence is more durable than certain forms of written matter. However, various cultural shifts or doctrinal regime changes can, in some cases, lead to massive destruction of any and all evidence of previous systems of thought. (eg. look at the official history of Buddhism in Thailand; then look at the archeology.)
It is a broadly complex issue.