PGP doesn't have plausible deniability. It actually has `you can prove anyone else what I said to you', if you sign anything. That's dangerous, so shouldn't be on tier 1.
(Or at least that's how it used to be.)
(Or at least that's how it used to be.)
I agree, but I don't see how that's relevent. This could be added to pgp, without "adopting a new, unverified cryptosystem"
Sometimes you want plausible deniability, sometimes you want to sign something for all the world to be able to verify.