SPARC seems to be shrinking as an architecture. As you say, processor R&D is very expensive. AMD has a tough enough time battling Intel, I don't think they want to be seen as competing with IBM's POWER architecture too.
I just don't see an upside for AMD. I doubt that Fujitsu and TI pay anywhere near enough upkeep to keep SPARC a viable platform on their own.
But it would certainly be interesting if it came to pass. :-)