3 scenarios I can think about:
a) domain names becoming irrelevant, due to new technologies and this sort of things. However, this scenario is delayed, thanks to ICANN. By introducing a bunch of new gtlds ( ==> a lot of $$$ spent by registrars and other related businesses) they in fact delayed it.
b) successful lobbying by verisign .com registry (variable registration and renewal pricing). In this case switching to domainer-friendly CCtlds may be an alternative, but who knows...
c) global cataclysms, planet X announced, etc etc. This or similar scenario where purchasing an aftermarket domain, or any domain, will become the last thing people will think about.