I have a very quick question...
People seem to be really wanting a rotating stage with clip-on matte-boxes. I wonder why. It is really easy to just rotate the matte-box itself until you reach the desired position (for your grad, pola etc).
At least, that's what I do with my clip-on matte-box. I place the filter in the desired position (more or less) and then I just adjust the clip-on unit until I reach the exact position I want.
Of course, maybe a rotating tray will make things slightly easier, but why go to the added expense/trouble when all you can do is simply adjust the matte-box. Since it is clipped to the lens already, it is super easy.