[iggldiggl]

> E.g. somebody could come up with the idea of running adb or an adb emulator on another phone, or even a small hardware dongle, integrating it with a pretty UI that looks like a regular app shop.

That idea already exists and is called Shizuku. You don't even need another phone, because ADB also has a mode for wireless debugging via the network, so you can just use that to locally connect to the ADB daemon running on your own phone.