It looks like this thread `TypeMap`: Generalizing `overload` semantics has more recent activity, a drafted PEP, and more concrete discussion, and I’ve had my questions answered here.
Unfortunately I’m new to this forum, so I don’t know the right mechanisms to officially mark this as the better thread to visit. On Stack Overflow I’d do something like marking this as a duplicate of that one so that visitors are more likely to go to that thread instead of this one if type mapping for generics is something they’re interested in.