To add to your list, there is also Secure Scuttlebutt  which has had a decent userbase over the past few years, and Planetary  which is a funded iOS client for it.
I think in general they all suffer from the chicken-egg problem and will need some reason for enough people to switch to be able to build a userbase. There isn't really any "novel hook" like tiktok, twitter, whatsapp, instagram, snapchat, etc have had in the past.
So I'll write my app outside of SSB, hopefully in a way that's mostly compatible, and possibly with future integration.
I may also toy with an SSB-like protocol myself, as the fundamentals of SSB is a work of art imo. I really enjoy what Gossip brings to the table, and how SSB focuses on human->human relationship to bring P2P to the table.