Isn't a platform migration the natural thing to do at that point? There is no "Power" in PowerPC, not in the year 2012 and beyond! ARM and/or x86, but not PPC! Since those features would require a break from the past, why continue with PPC at all? Why not bring the new platform onto a modern architecture? For example, if MorphOS developers would want to start exploring 64-bit support for the future (as suggested by Fab in his presentation of MorphOS future), why would they do that on a *dead* G5 platform (or PA6T for that matter)? I mean, if the legacy is to be broken anyway, why not migrate to greener pastures while you are at it?
Clearly the only sensible option is to migrate to modern operating systems with plenty of software support. Take your choice Windows, OS X or Linux.