> There's a race to replace JWTs with something better (PAST is an example) and while I don't think the underlying idea behind JWTs is any good either, even if you disagree, you should still wait for one of the better formats to gain acceptance.

Aside from PAST, I recently have come across this[0] (called branca) as I too was looking for an alternative to JWT. This seems to be based on Fernet, but according to the maintainer of this spec it isn't maintained anymore.

[0] https://github.com/tuupola/branca-spec