It's probable that licenses that explicitly allows revocation at will would not be approved by OSI or the FSF.

Copyright law is also a complex matter which differs by country and I am not a lawyer so take this with a grain of salt, but there seem to be "edge cases" where the license can be revoked as seen in the stackexchange page below.

See:

https://lists.opensource.org/pipermail/license-discuss_lists...

https://opensource.stackexchange.com/questions/4012/are-lice...