I think if too many asics start to mine, people would just switch to asic-resistant currencies with different algorithms like vertcoin or something with scrypt-jane, wouldn't they?
That is a very real possibility, yes. It is uncertain how profitability will fare on those currencies though regardless of being ASIC resistant.
I just invested in 30 290x mining farm and just got them up and running couple of weeks ago. I now feel that it's too late and that I should have known and invested in Gridseed instead. Now I'm wondering if should take the loss by selling by GPU rigs now to convert to ASIC farm, gridseed in particular, but the one major speculation I'm hoping for is that GPU mining will continue to be profitable because of nscrypt. Then again maybe nscrypt will eventually work on these asics...