Mumble is a third party, voice chat application, with OSD and in game positional Audio. So you can't deny the ability to make music bee positional to an extent.
The now playing only works if a game is windowed, it would be wonderful to have a in game now playing option.
Media keys hardly work in any games, especially now that steam added a music player. I would really like to be able to change my songs while playing video games.
You may be wondering, why not use a ingame audio player in GTA for example, well I don't because I'd have to duplicate my library into its folder, and my library is huge, also it doesn't support my file type and you can't skip songs. Why don't I use steam music player? Steam only supports MP3, no multi channel audio and the library explorer is rough at best.