I’m honestly unconvinced that the “or later” clause of the GPLv2 license is legally valid. Can anyone think of any example where contract terms get to be reinvented by a self-interested third party whenever they choose?

The "or later" is a separate issue, I think.

IIRC, the FSF generally insists on getting assigned the copyrights on all GNU software, so the FSF can re-license any new version of their software under any license they choose to, which is currently GPLv3.

Users/vendors can still choose GPLv2 for the older versions of GNU software, which I think is what Apple does for the few remaining GNU software they ship.