Guess what? We just released flutter_soloud version 2.0.0!
There's still a lot to be done but we don't plan any major API changes anymore. (There was an _insane_ amount of those between 1.2.5 and 2.0.0, as advertised.)
If you "just" want a proper audio engine for Flutter with support for gapless looping, filters and low-latency playback, then 2.0 should fit the need. This should be enough for most games.
https://pub.dev/packages/flutter_soloud
Thanks @marco_bavagnoli!