2.15.30 works, however, at least in OS X Sierra, it was not stable at first and often crashed after adding content. Not sure wether it's audio analysis. I disabled that in prefs and then was able to do an encoding. Now, today, I didn't experience any crashes.
More important: The Scale To: 'No stretch' and 'No scale' now works as expected with non-square pixels (or, at least with 2:1 pixel aspect ratio as far as I tested). The screenshot here this time is real, not photoshopped. And the resulting DCP looks as expected.
Anything and everything to do with DCP-o-matic.