Well, I seem to have developed a workaround. DVD Styler has the abilities I want — multiple subtitle and audio tracks, fully custom menus and disc structure, etc. As you can tell from the name, it doesn't natively do Blu Rays, but what it can do is make a kind of pseudo-DVD disk image, using the DVD file format but with HD video and not limited to the size of a DVD. I should then be able to use a little converter utility (which is Windows-only, but I can borrow a PC for this short, one-off step) to convert this pseudo-DVD disk image into a proper compliant BD-25.
I've got most of the features ready, including the Matrix preview, a couple of featurettes, a subtitle track (with a couple of extra gags thrown in — it'll also be included in the .info dlc as a standalone srt file), a trivia track highlighting what I've done to the movie, chapter markers, and the menu design itself. The only thing left to create is the "TV safe" audio track, which I hope to do over the weekend.
I expect the actual authoring process will be a right pain, and it is a bit of a hack that I'm using, so I can't make any promises. But it at least should be possible.