Chat apps have a heavy reliance on network effects, self-hosted solutions will not be able to cut it.
MLS on nostr is promising, and perhaps the only possible solution to this problem.
Discussion
What is MLS?
Messaging Layer Security. It's a protocol for encrypted group messages, so far it has required central servers, though nostr:nprofile1qqspwwwexlwgcrrnwz4zwkze8rq3ncjug8mvgsd96dxx6wzs8ccndmcpzemhxue69uhhyetvv9ujuurjd9kkzmpwdejhgqgcwaehxw309aex2mrp0yh8xmn0wf6zuum0vd5kzmqpzfmhxue69uhhqatjwpkx2urpvuhx2uctyqxu5 has figured out how to do it with nostr and we have whitenoise which is kind of like signal on nostr.