First of all i think ML will work on 6D perfectly.
But 6D has serious moire and aliasing problem on video mode. And ML can not fix it. It will be good still camera. But AF points are problem. I thought video quality will similar as Mark III. But it's not. ISO and bitrate(ALL-I) better than Mark II. But that's it. Bitrate is not problem for ML users. So just ISO performance is better than Mark II.
But 6D has serious moire and aliasing problem on video mode. And ML can not fix it. It will be good still camera. But AF points are problem. I thought video quality will similar as Mark III. But it's not. ISO and bitrate(ALL-I) better than Mark II. But that's it. Bitrate is not problem for ML users. So just ISO performance is better than Mark II.