Whatever limited drop in difficulty may occur, it will vanish as soon as the first ASIC rigs are delivered. In the end, if ASIC would be far away on the horizon, most would already have switched to FPGA rigs in order to remain profitable with the block reward halving. I am actually surprised that overall, few big time GPU miners did not do a full transition to FPGA months ago in order to reduce their electricity drain.
I think in my case it depends on how much u invested in GPU,s and before u ROI those again invest in FPGA,s just for the electr. cost didn,t make sense to my situation because the gpu farm was steady making BTC month in month out and mining for the long run nowing that the BTC become more wanted in the coming years ..you could say i skiped the FPGA ,s and i am glad i did they out runned in a very fast tempo when ASIC hit the net..and gpu,s are much easier to resell if necessary but i will transit to an ASIC rig but only when i see ASICs doing 60gh@60watts in the wild untill then i just keep mining oldschool...and i think more miners think this way..
