Overall, I agree that the PEP is pretty complex to implement. However, features like concatenation of variadics are crucial for typing common tensor functions (which is the underlying motivation behind the PEP).
Would it be better to split this into smaller PEPs?
1. Variadic tuples with no `Map` and no concatenation of variadics
2. Concatenation of variadic tuples
3. `Map` and other higher-kinded types
Can you clarify what "no concatenation of variadics" refers to? Does this mean we can't (yet) have `Tuple[int, *Ts]`? Or is that specifically about `Tuple[*Ts1, *Ts2]`. (And what about the same constructs inside `Callable[[<here>], R]`?