I don't think it's feasible to change rules about tuple type compatibility at this point. Existing type stubs (including typeshed stubs) assume the current behavior. It's especially important for function overload matching. If we were to change the rules and make open-ended tuples assignable to fixed-sized tuples, the selected overload would change in some cases.
I also agree with Guido's justification for the current behavior (in the case of tuples). So even if it were feasible to change the behavior at this point, I don't think it would make sense to do so.
I'm not opposed to adopting different rules for (non-tuple) variadic generic classes if we think that the target use cases justify it. Of course, all things being equal, I'd favor consistency. Hopefully that's not considered a "foolish consistency". :)
-- Eric Traut Contributor to Pyright & Pylance Microsoft Corp.