You assume the problem is hardware limitations... Hardware means nothing if the limitation is in how the software is designed and engineered. For example, they seem to want to create a very sophisticated AI for your companion... Anyone that has dealt with the girl from ICO knows a great AI would have made that game a lot more fun. If that is indeed part of the problem, no matter how much processing you toss at it means nothing if you can't get the AI to act how you want. And that's just one very small facet that could cause an issue...
As far as I know, team ICO is also still a relatively small team and the original creator of the game has since left adding even more disarray to the whole situation... in fact, if Team ICO is really as small as I remember hearing it is, then the switch to PS4 may be even MORE damaging (having to redo assets, adjusting to buggy new SDKs, all new rounds of optimizations, etc). It's not like working on a PC where you simply put in a faster graphics chip and the same game suddenly plays better. It's a whole new architecture that would require at least a decent amount of rewriting.
