According to Link, with regards to std::tuple...
libstdc++ always places the members in reverse order, and libc++ always places the members in the order given
Assuming that's true, is there a reason (historical or otherwise) why libstdc++ uses reverse order?
Bonus: Has either implementation ever changed its std::tuple ordering for any reason?
See this answer for why libc++ chose forward order. As for why libstdc++ chose reverse order, that is probably because that's how it was demonstrated in the variadics template proposal, and is the more obvious implementation.
Bonus: No. These orderings have been stable in both libraries.
Update
libc++ chose forward storage order because:
In short, the implementor of the libc++ tuple
merely felt that storing the objects in the order the client (implicitly) specified was the quality thing to do.