I suspect retrofitting a whole new identity system to Fediverse will never happen because server admins, or instance admins, will come up with all kinds of reasons why they don’t like the idea of not knowing who their users are. Some of them would probably allow it, but I bet a whole bunch of them wouldn’t, and we’d get into this fragmentation where some servers won’t allow posts from those types of identity, etc. It seems to me much easier to take Nostr and just give it the functionality you get inside the Fediverse.
Mine is 1Password mainly because I really like the way they handle Security by forcing you to use a key that they issue you that we know is very secure because of its length than randomness. It also has the best ui of the ones I have used.