Are you able to play your bluray content on MC for Mac at all right now? I ask because bluray menu support implies that you have bluray ISOs that you want to use, or that you want to play bluray discs directly. MC for Mac does not support disc playback of any kind right now.
As for ISO support, I don't think you can do much with a bluray or DVD iso, as MC doesn't seem to recognize them at all. Most importantly, MC for Mac has no way to interact with any video source that is encrypted with DRM. This means that pretty much any commercial DVD or BluRay video file is not playable on MC for Mac.
On Windows, MC relies upon 3rd party tools and programs that dynamically decode the encrypted (DRM) content from these discs or ISOs and let MC play the unencrypted versions.
On Mac, MC is happy to play unencrypted files that came from DVDs or BluRays though. I have used MakeMKV on hundreds of DVDs and BluRays to produce unencrypted, (no DRM) clear video files, at perfect quality, and MC plays them back without issue.
There are, of course, no menus when you rip individual video files (titles) from DVD or BluRay, but I think that's mostly a positive thing! No more waiting on menus. No more navigation hell. Just straight to my video and it immediately plays. The only real down side is that it makes handling special features, and alternate versions more difficult. But I'm not really big into those things. They are neat I guess, but I don't really care much about them. I'm mostly interested in the movie (or TV show) on the disc.
Just some thoughts.
Brian.