I agree that anything we can do to make the development of xmaps easier for power users will ultimately have a big benefit in the end for all users. As for the current state, please do bear in mind that this is still all in a very early stage. As your questions indicate, this is a hugely complicated area with many special cases. We are introducing functionality incrementally so that we can get feedback from the community as we go along (rather than create the full implementation and then find out doesn’t meet everyone’s needs).
As I may have mentioned before, the whole area surrounding multiple concurrent techniques and how they get resolved still has a lot to be done. We’ve not fully established the rules for mutual exclusions, priorities and fallbacks. Once we do I hope the behaviour will be a little less mysterious.