64 gb itouch would be at the 600 dollar price most likely, which i dont think would perform well on the market. if they do release a new touch, i dontthink it would be much different from the first touch.
In my opinion, you won't see a 64GB iPod touch until a 32GB iPhone exists. Remember that the iPod touch uses two flash chips while the iPhone only uses one. My contention, therefore, is that when it's cheap enough for the iPhone to have a single 32GB flash chip installed, it will also be cheap enough to have two such chips installed in an iPod touch for a grand total of 64GB of flash storage.
Of course, I may be on the opposite side of correct - only time will tell.