YACoin was always intended to be a CPU coin. Now that it has become a CPU coin we want to change it? That's nuts!
That's actually the problem. After the last NFactor change, (as you mentioned) Yacoin is for the most part a CPU only coin now. A huge majority of the network was POW mining using GPU's before that, which was a disaster waiting to happen. Someone is currently using a botnet or something similar to make a lot of BTC trading YAC for CNY on Bter. They seem to have had this calculated and ready way before we moved to NF 17, so bully for them I suppose.
So yes, whatever change we implement to fix this issue will have to take into account that, going forward, Yacoin is essentially a CPU only coin.