I'm not trying to solve your problem.
I want to know why you consider this InterfaceUnion necessary when all of these methods are already availble.
So, would an InterfaceUnion serve any purpose? If so what?
As for +1, -1. None of that matters.
The only person who decided what goes in is Fred. If you want it, you have to convince him that it would be a good idea.
That requires effective discussion, not a bunch of posts with numbers on them.