I'd settle for full sync of chats between my own devices. If I can sync between my laptop and my phone, that's sufficient, since I already back up my laptop.
I don't want backups for IM. I don't want my counter-parties to have backups for e2e encrypted IM. I don't want IM to last. Why record every conversation on your permanent record? It's nuts.
For me, having a searchable record of everything said defeats the whole purpose if IM and e2e encryption. I'm sure the NSA like it.
The lack of any kind of backup/export for iOS is the main thing keeping me from recommending Signal.
Sadly, from what I’ve seen in similar threads online, it seems the devs are opposed to backups in principle (they believe that chats should be ephemeral and backing up is antithetical to this).
I‘ll take it. Even offline backups would be an improvement.
For people worried about having not consented to other peoples backup. They could implement ephemeral-only chats, or backup-excluded chats where both parties have to agree to changes.