Actually, what could stop .XXX is what was expected all along: Countries blocking it.
India has already announced that it will block .XXX.
http://blogs.forbes.com/michaelhumph...stry-hates-it/
It is very likely that the standard governments in this sort of thing step in. All of the middle east, Australia, New Zealand, possibly the UK, Russia, and such are likely all to step in with blocking on this TLD.
If you are buying an overpriced .XXX domain, you are flushing your money down the toilet.