Well if one wants prisms... If I were to add the prisms, I would remove the mount mirror and the pbs, add a plate in front of the knife edged beams for the prisms and the bounce mirror and pbs/mount. sort of like an optical lego. Going on that line of thought, I would also split the octo into two quads in the same design. One thing I would like to see on most new plates is a U-slot rather than just a bolt hole, I like jiggle room!
-Adam