And thus accelerates Google's push away from APKs, preferring instead for all developers to embrace their proprietary App Bundle format. Complete with ad hoc signing performed by the Google Play store at time of download. The bundle is also customized to the device, meaning an .aab file ripped off a device won't necessarily be loadable on another device since it could have different configurations/hardware that happen to limit it.

I think anyone who works as a dev knew this was Google's endgame the moment they started circling the wagons with the app bundle stuff. It was already getting weird before that, but it was uncharacteristically out of step with historic Android.

Nope, you could, given that no Google libraries is used.

You could always run the APK on a stock AOSP build, or any fork of it in the internet.