Hi David.
I was just writting a post now, trying to explain too why offscreen rendering won't help us on this case, and got your new mail while writing it, so here I start again... ;-)
I think your new suggestion is quite interesting, it sure is more general than BTF / FTB, although I personally don't see any useful painting order except BTF / FTB (of course, the fact that I personally can't find any doesn't mean there aren't any).
I mostly prefer the more generic implementations, and this is why I prefer your way over mine, although implementing 3d in this way will really be harder. I volunteer for trying to do that (and transparent cube too), if you are interested.
What do you think of all the other patches? Do they look okay?
Thanks,
Roi.