I’d love it if Signal officially supported UnifiedPush, it seems to be the most promising direct alternative to FCM. They started talking about quantum-resistant encryption or whatever, but at the same time resorted to using a websocket.

Which is pretty much the least elegant way of doing it. Not something I’d expect from them, to be honest.

Then there’s Tuta Mail, they have a much better way of handling push notifications, but it’s still their own thing too, and instead of promoting something like UnifiedPush, they write blogposts dragging Protonmail for not having an alternative.

(Which I’m also annoyed by, but their posts about it seemed a bit pretentious, which I just hate to see.)