This is one of the areas in the high level design that is the least specified.  I love to see a doc on how we want this to work (both short term and long term).

For clarity, I think this particular bug tracks two things:

- ui_scene shouldn't care about OpenGL stuff
- The VrShellRenderer types should be able to efficiently draw multiple elements without breaking each other (there was some fragile flushing logic put it that ought to be solidified)

Obsolete.  Much of this refactoring has already happened, or has a line-of-site to completion.