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.