I wouldn't be surprised if eventually an implementation for GPUs came along that was optimized and destroyed CPUs for efficiency and speed.
+1
There's no way to [proof] proof anything forever... Unless WM wants to spend the time/effort to constantly try to stay ahead of GPU implementations...
Personally, I don't see a reason why eventual mass GPU YACoin mining would do anything but strengthen YAC as it did for LTC. Besides, there are going to be "lots" of vid cards sitting around looking for something to do once ASIC's completely take over Bitcoin.