I asked for this way back in the MC 13 forum, thought I'd ask again:
Support for sidecar audio files. Zoomplayer had this way back when I used it for video. Which means the possibility to play back a for example a flac or DTS-HD audio file with a mkv video file without having to mux them together. It's already possible for subtitles, so why not with audio?
One possible scenario that it would be useful is if I have a ripped Blu-ray, then I get a new edition with a similar video stream but better audio (or a new language), I could just rip the audio from the new one and play it with the old rip, and even delete the old audio file if I don't need it anymore, since I would have the possibility to keep all my BR rips as separate audio and video files.
Also, by muxing the DTS core into the video file and keeping the DTS-HD separate I would save space when dropping some movies on the tablet's memory card for watching on the go. A DTS-HD track can take 5-6 gigs, which is a lot when using 16/32/64 gig memory cards.