The Zune upgrade bounty exists because AROS has decided to use Zune as the defacto GUI toolkit, and updating the API should help to port whatever apps depend on newer features (I still haven't seen a good list of what those features are anywhere...)
And yes there are those who would love an open source clone of the reaction API to make porting code easier to AROS from OS4. Anyone can start a bounty like that if they want to. It doesn't mean anyone will actually take it up though.
Personally I'd like something new and different, that focuses on integrating outline fonts, stretchable bitmaps and structured drawing primitives (for more resolution independence and printing support), with the possibility of animation and 3D engine enhancements for extra eye candy appealing multimedia stuff.
