Why would OS4 (or MorphOS for that matter) be more succesful than say BeOS ?
The PC market is Microsoft's, the PPC market is Apple's. The leftovers are for Linux.
They are going to have to come with something quite amazing to even make a small change to that. We are all Amiga enthousiasts here and that may warp our view. The outside world couldn't care less about Amiga, it's OS etc... As things stand now we will be lucky if our new "Amiga" (again no preference for blue or red) can do everything a PC and a Mac can do, preferably with the same quality or better.