I know I've been a bit of a lurker since this discussion got resurrected but:
2. RE: variadic=True, I'll echo an older comment of mine that "variadic"
is a bit of mouthful and hard to spell. Instead we might consider
something less technical like `tuple=True` or `many=True`.

The thing I like about a mouthful like "variadic" is that if you encounter it and don't know what it means you know you need to go look it up. If you see "variadic type" a google search is going to lead you to answers; if you try that for "many type" or "tuple type" it's not.