Not sure what you're referring to: I don't see any `mpv` package in NonGNU ELPA.
Hah, sorry, I got a little confused by something else. That's right, no mpv in NonGNU ELPA, so not a problem then. It's not a dependency anyway, although that does mean that for the best subtitling experience, people will need to install mpv from that other repository.
... Is the mpv package the sort of thing that might be considered for inclusion in NonGNU ELPA? :) It would be pretty neat to be able to let people package-install and get all the useful parts, although they'll still need to install the actual mpv player separately. (At least until that Emacs-based video player gets all sorted out...)
> Is it okay for ELPA packages to depend on NonGNU ELPA?
Yes!
Okay, I can try asking the other contributors. Might be a bit of a low probability, though, but worth a shot.