IV is a compilation? IX was a compilation of the first VIII, but I don't remember anything like that ever being said about IV.

As for FFXII and its influence, while FFXIII looks like it's going to have turn based combat and vXIII is going to use the Kingdom Hearts system (or something close to it), it looks like the whole 'real-time' encounters thing have made their way into White Knight Chronicles. So that's something, at least.