Scratch does it and it's GUI preview is also 10bit. It's done over OpenGL.
Flame GUI preview is also now 10bit- not sure if color accurate.
It's not impossible this is the point.
Cheap yes, reliable- well, I would argue
I would be actually happy to pay bit more for improved reliability (specially from drivers/SDK side).
SDI cards are now nothing special like they use to be old days. Todays consumer technology quite often surpasses pro one and SDI cards can be "replaced" if needed. Modern GPU have all needed technology there and DP or HDMI is all what you need for most small studios.
I understand BM approach, but this is BM specific case, not a general one.