[popcornmix]

I didn't look into this at all, yet, but my assumption would be that we can just use libbluray to get access to the main SSIF, the same way we get access to the main M2TS, can't we?
Beside the menu things, I see libbluray as a filesystem accessor, but I can be completely wrong.

I've not dug in too closely, but my understanding was that libbluray currently opens the (left eye) m2ts file and needs to be changed to open the ssif file, so some changes to libbluray are required. I had imagined merging the left/right nal units to be done in libbluray, but no objections to doing it in dvdplayer's demuxer if that makes more sense to you.