One thing can be done now to help compatibility - provide Hildon alternatives/wrappers to the patched GTK+ versions (like tap_and_hold company) in one of the next updates. Keep them later in MeeGo. Inform the developers that the previous ones will be deprecated.
There. Easy.
If I am correctly following what you are saying, we don't know if MeeGo will accept Hildon alternatives/wrappers so it may not be that easy. Is a fork just as easy, is it desireable?
3-time Maemo Community Council Member
Co-Founder, Hildon Foundation