Will PPC programs written for AmigaOS4 run on MorphOS? I don't know about that; probably not, I guess. But it remains to be seen which platform is supported better. Amiga, Inc. has the brand name going for it. But MorphOS seems to have quite a bit of third-party support lined up as well. It'll be interesting to see how the applications come for each.
ultiamtly it isn't going to be an Amiga.
This only matters to (some) current Amiga fans, and there aren't enough of them to support
any new computing platform. The only way either AmigaOS or MorphOS can survive longer-term is to win over new users and new developers one way or another. How well that goes depends on the details of the operating systems themselves, and on how well the companies attract and support third-party developers. Time will tell.
-- gary_c