> Consider for the sake of argument, what might happen if some very
> important piece of code starts using the copyleft-next license, and
> then whatever organization which is handed the responsibility of
> maintaining the copyleft-next license releases a new version which
> basically says, "new rules!  copyleft-next-v2 == new BSD-style license"

In the context of a program licensed under "GPLv3 or later", I remember someone asking RMS that question during one of his public talks. Unfortunately, I can no longer find a reference to his exact answer but my recollection of it is that Section 14 covers that:

"Such new versions will be similar in spirit to the present version"

A non-copyleft GPLv4 would not be similar in spirit and so the  "upgrade clause" would no longer apply.

It does feel like a fairly weak protection though.

Cheers,
Francois