> Especially after SyncThing disappeared from Play Store (because it was basically a non-Android app behind a thin Android shell that couldn't easily be upgraded to more modern native APIs), there's nothing super-obvious here.
That's not what happened, it was Google who started rejecting their updates on Play store. I believe the original Android app maintainer quit after that but there's a fork on on F-droid which works perfectly.
Assuming that the developer of Syncthing-Fork doesn't mind providing ID to Google, they shouldn't have an issue getting a signing key (we will see how this works in practice). They aren't doing anything objectionable to Google.
The bigger issue for third party apps will be things like Newpipe, where applying for a key will put the developers in danger of a lawsuit because it affects Google's business.
(The APK signing requirement is a fiasco, I'm not defending Google. Just pointing out that this app will probably not be as seriously impacted as others).
That's not what happened, it was Google who started rejecting their updates on Play store. I believe the original Android app maintainer quit after that but there's a fork on on F-droid which works perfectly.