@southsamurai Oh that's definitely a huge concern, but not just for self-hosting but for privacy in general.
But still, if the average joe wants to self-host something using an old phone is probably the easiest way to get them to try self-hosted alternatives and drop corporate / commercial services.
Maybe not the 'average average joe' such as my parents, but anyone who is minimally curious enough to do stuff such as registering a domain, setting up a game server for friends and maybe has opened the CMD windows console once or twice in the past following a tutorial. That kind of demographic (IDK if it has a name) might be much more inclined to self-host if it was as easy as installing an APK and letting your phone one somewhere at home.
Overall as long as Android doesn't become straight out malicious spyware itself, the benefit of dropping commercial alternatives might very well be a net positive. In a worst-case scenario, any tunnel / vpn configuration necessary to expose a service to the internet could also add an automated step to blackhole requests to google's tracking servers.