I don't think the aim was ever to replace MUI4 on MorphOS, and I really don't think it's anywhere near as big a deal as some of the arguments are making out. With a Zune compatibility layer on MorphOS and OS4, it makes it very easy for a developer to write an app for all three platforms. MorphOS itself and all the existing and future MOS-only apps can still use MUI4 for what they need, muimaster.library and what not, and any apps compiled with Zune header files can use the similar-but-different z_muimaster.library. It doesn't interfere with the system at all, but offers an extremely easy route for porting apps between all systems. What's not to like there? Or do some people have a fear of not having a "pure" system or something?