Only to realize in the process that all I really needed was to modify the shader program's depth checking behavior. Even just disabling it altogether looks fine and makes everything way faster. Never in my wildest imagination a year ago would I even dream of implementing WBOIT in one night and then just leaving it in a branch for a one line change.

In the process I realized a little trick on my own, using what I learned, to modify the depth values a in the fragment shader would let me selectively translucently blend/occlude stuff. Basically the idea was to put stuff I wanted to blend order-independently all at an equal z position and then to set the depth function to "less than or equal" instead of "less than". I used the occluding geometry's depth buffer as a source to modify the translucent stuff's depth buffer in the fragment shader.

There's absolutely no way I'd have had the guts to try all that in one night without the robot tools.