I am looking for this type of stereo, too. I even purchased a low-end quadro card to see some progress (on FreeBSD). There is no technical reason why active strereo should not be possible on non-quadro cards, IMHO. ALL you need is be able to swap pages at each vertical retrace.
Copying a page should not be too expensive (but this is not needed too much, because only the stereo window is likely to be updated very often).
I don't have much hope to see progress in this soon, as nVidia seems more to care about trade secrets than their (potential) customers.
For me, it seems feasible to add the basic page flipping machine to the XFree86 nv driver.