I worry about this kind of thing even with my family who are filled with tech elites. Being tech savvy does not mean being security savvy. The amount of times I've had to convince my family that yes, you do have to update your OS, your devices, your password manager, etc is maddening. Hardly anyone cares about security over convenience.

I foresee that Meta will make a dedicated landing page with a side-load download + easy steps and it will get adopted by a size-able chunk of people (like you say). Once that side-loaded app is on the device, they will have auto-update features built-in and you'll likely never need to manually install it ever again. They'll essentially have complete rooted control over your device and use it to steal any and all information possible.

This is a very real reality and I don't think folks care enough. I'm not even against opening up the app store(s), I just wish we had regulated social media's permissions to our private life more before we opened the flood gates to the garbage they will now attempt to dump onto our devices.