The current 3D situation is fairly well summarized by Adam. Except the "non-official" bit - arithmetic functions in BG are absolutely official and public.
I will add a cross product operation to the library - that's honestly the only building brick I can bring in a reasonable time right now, as I still have to finalize the work on variants (only 2-3 algos left). A "normal" algorithm is planned but no ETA at all yet.

More generally, I'm basically the one who was supposed to bring the 3D bits into BG - being mostly the only author really interested in that. I just have troubles finding the time for that, and even more because I work on more general features.