> A variable int tuple, for example, can be typed as Tuple[int, ...].

That's a type that matches tuples of any length, not a variable-length tuple. The size of a tuple can't be changed. A variable-length tuple doesn't even really make sense, what you'd want there is a list.

> You can't concatenate two variable-length tuples, which makes sense - where would the cutoff be? But you should absolutely be able to concatenate two fixed-size tuples, and it's very limiting that you can't.

This whole statement doesn't make sense. I'm assuming you're still talking about type definitions and not actually tuples.