It seems #ListenBrainz might be what I am looking for. Will feed it some nonsense through the Android app and see how the recommendations work.
I hope scrobbling from dedicated music players (e.g. using #RockBox firmware) and bidirectional integrations into desktop apps will work as well as from the phone soon.
If anyone is interested, this is me now:
https://listenbrainz.org/user/hook