In principal I don't see anything preventing it. You can run rust on it. People have managed to run postgresql and even docker on android. So all the requirements are there.

I'm sure running it would be possible technically.

I think the main challenge would be federating, since most people's Android devices don't have a permanent IP address, and mobile bandwidth can be more expensive. Also, mobile carriers may disallow running a server.

If you only ran it from home on Wifi, sure - but then why not run it on your PC?