Mkv now works but only so and so, with sound even. Mobo player plays them. This may require mvideoplayer also installed, they appear to share something related to codecs perhaps.
Also, newest version of es file explorer today added mkv support, which possibly only has to do with it's own internal player, or is perhaps somehow involved in the suddenly much improved mkv playback. Best bet maybe to install all three, play after a fresh boot for maximum free resources.