What you won't be able to do is federate with the official servers.
Oh, and there's also a WebSocket transport (used by the Desktop client) that doesn't involve Google. That just doesn't provide a pleasant experience on mobile.
I'm sorry, but is this a joke? "To not use a centralized server that you can neither audit nor trust, you have to recompile the client, but that's easy?"
This smacks of "oh, PGP for email is fiiiiiine." To say nothing of the silliness of the inability to federate.
Don't casually disregard him because you or others can't understand basics of doing what it takes to alter and run a service in your own private space.
I don't need Signal to communicate with knowledgeable people. We need something to communicate with everyone else.
The moment you open the door for federation, the protocol is written in stone forever. All it takes is one server in the federation network with a substantial user base that chooses not to update. (See SMTP).
OWS decided that relinquishing the ability to force updates (i.e. away from a broken cryptosystem) would sacrifice too much in the way of security to be consistent with the project's goals.