This is my suggestion for a future RMX release.
An immediate key switching in musical groove that have a base key (the original one). I know it's not easy with the current instrument architecture. First of all RMX should be aware of the original key of the groove and I don't know if, for example, a rx2 conversion could give this info.
The switching of course could influence only the base key, not the quality (major, minor, 7th, etc.), and should be effective immediately pressing a key on the keyboard or recorded on a midi track. In conjunction with Time Designer could make RMX the definitive virtual instrument.