[Ace]

not hiding wouldn't give any benefit when you try to turn of subs again by using ACTION_SUBTITLE_NEXT mapped on your remote. Or we don't hide them, but a) rearrange and b) skip them in cycle actions but be still able to choose them directly

I really don't like hiding too.

...(btw - we should change the spinners in the video/audio OSDs to lists)...

That's on my list for a while

A per-video setting window where you can enable/disable subtitles and audio tracks?

Seems to be too complicated. What's already in is that once you have configured the languages the settings are saved (per video) when you stop playback.
One thing I can think of is a optional "nag screen" before playback starts that prompts for the audio or subtitle language if auto selection fails.