Forward secrecy is not of any real value in most instances of instant messaging as people usually keep their old messages around thus negating it.
Using OpenPGP in the way that TLS is used would negate the advantage of static encryption and would cause the result to be as insecure as TLS. Probably worse as OpenPGP has not required all the band aids that TLS has ended up with.
> Forward secrecy is not of any real value in most instances of instant messaging as people usually keep their old messages around thus negating it.
Both Signal and WhatsApp have disappearing messages as a feature. Signal now allows users to enable this feature by default for new conversations.
Most people keep their old messages because they're only aware of some remote dragnet surveillance threat in democratic countries. I'm sure the situation is different in countries where the surveillance is more offensive, and perceived so by the population.
Encryption is not of any real value if the threat you're describing is 'someone simply has access to all your plaintext messages'. This isn't a meaningful argument against forward secrecy.
The argument is that an attacker that gets your secret key material also gets your saved messages. If you had a more secure way to protect the saved messages then you could of used it to protect the secret key material. It is more or less the same problem.
Using OpenPGP in the way that TLS is used would negate the advantage of static encryption and would cause the result to be as insecure as TLS. Probably worse as OpenPGP has not required all the band aids that TLS has ended up with.