The only fly in that particular ointment is the not insignificant problem of space - there is no room in the casing for a discrete graphics. That was the reason they didn't get one last time around. There has been discussion about this last year. A couple of reviews also highlighted this was the case.
True, but not exactly. The current Mini has 2 chips; the C2D + M320.
Sandy Bridge is a SoC architecture so this has been cut down to just one chip. The space left by the M320 could be used by a discrete GPU.
However, the problem I see with this is whether or not there is space for the dicrete RAM for the GPU, not the GPU itself.