> One other note, the equal-number-of-senators-per-state is the one thing that the Constitution explicitly forbids changing by amendment, the last clause of Article V.

It doesn't forbid it, it just requires states losing equal representation to consent to the change.

Of course, it also doesn’t limit, say, reducing the powers of the Senate, including transferring them entirely to either the House of Representatives or a new third house of Congress, leaving Senators as purely decorative fixtures.