Honestly though, if Canon pulls off 8 stops of IBIS with the unstabilized RF 85mm F/1.2, why even bother with IS? We know from Canon that the larger aperture lenses (28-70, 85mm 1.2, 50mm 1.2) give IBIS more room to work, which gives better stabilization.
Consider that the EF 85mm F/1.4L IS had to literally have the IS unit from the *400mm F/2.8* just to have IS with such a wide aperture. I'm sure the IS unit is one of the most, if not the most, expensive parts of the EF 85mm F/1.4L IS.
If Canon has the 85mm F/2 IS for $600, and the RF 85mm F/1.2L for ~$2500, I think they could easily make a $1100-1300 RF 85mm F/1.4L. If someone really wanted mechanical IS in the lens, they could always use the EF version. If this was the case, I could see the RF version being released for cheaper, than the EF version, since it wouldn't have IS built in.