Thanks PhiKoen, I didn't know Antox. The point I was trying to make is that we can never know what happens in the future. What if the members of the current Signal foundation give up on the project and become replaced by people who decide to monetize it with ads, track their users, ... If that happened and you decided to start using something else then you lose all your Signal contacts and have to start from scratch again. Decentralisation neatly solves this problem.

PS: XMPP/Jabber is fine. I used it a long time ago but I didn't like the issues it had when logging in from multiple devices at the same time. As far as I know they haven't fixed that yet.