Feallan said:

Exactly, Blu-ray format means limitations. With MKV number of audio tracks is not an issue. Unless Harmy gets access to better software, I think MKV is the best bet for next release.

Well, Blu-ray with menus has limitations. If he wants to make a menuless Blu-ray with tsmuxer, audio tracks are unlimited.

With MKV, he's been avoiding PGS subtitles and including SRT subtitles for player compatibility reasons. I think there may also be compatibility issues with certain lossless audio formats on MKV too. So, a menuless Blu-ray may still be effectively better than an MKV in a couple areas.

But it's worth waiting to see if there are other authoring options, of course.