I don’t think it is a good idea, it doesn’t matter much it is not backwards compatible, people can always upgrade if they want to see the name, storing a name there will be leaking a name forever even after name changes etc. besides over-complicating implementation for something that is bound to become useless
It’s a good point against embedding the fingerprint in the message itself (which is not needed to get the notifs for mentions)
No, it’s the other way around. The fingerprint of a profile won’t change, while the display name and the email address can be changed back and forth any time. Hence, embedding the fingerprint according to my suggestion would be a stable reference to the given person.
You could use name+“relative id” in the message text and put “relative id to fngerprint” mapping in the encrypted message headers, there it can then easily be removed on forwarding without parsing the text.