I actually think the 85mm f/1.2L II is in more need of replacement than the 50mm f/1.2L.
I adore the output of the 85mm f/1.2L II but it has some major shortcomings that make it a difficult choice for general use unlike the 50mm f/1.2L.
Reasoning:
1. 85mm f/1.2L II really needs focusing speed improvement. I understand that there is a lot of glass to move, but perhaps they should do what they did with the 50L and make the mkiii a 85mm f/1.4 if that would solve this problem. It is a bummer to use this lens at a wedding and fail miserably with even center point AI servo because it can't keep up. The 50mm f/1.2L is not a speed champ either but it is more manageable in terms of focusing speed than the 85L.
2. 85mm f/1.2L II would be nice if it had weather sealing w/ filter like the 50mm f/1.2L. With the current design I think weather sealing is simply not possible due to the way the glass is moved around.
3. 85mm f/1.2L II has been known to break more frequently than other lenses due to the fragile-ish motor that drives the front element. Again, maybe downscaling this lens to a 1.4 could solve this as well.
In summary, I'd like to see Canon do what they did with the 50mm f/1.0L > 50mm f/1.2L. The 85L is surprisingly similar to the 50mm f/1.0L, so making this sort of revamp would not be a big change. I don't think it is world ending that you can only get f/1.4 instead of f/1.2, and fixing all of the above issues will make the 85L f/1.4 III much more usable in general.
An another note, yes I know the 50mm f/1.2L has much more focus shift at MFD than the 85mm f/1.2L II. But the 50mm f/1.2L also has a much shorter MFD, if you backup to the 85L II MFD the focus shift isn't much different. Also note that the 50mm f/1.2L is sharper and has less visual anomalies than the 50mm f/1.0. Perhaps the purple/green fringing can be reduced if the 85mm III is made an f/1.4.
In summary, Canon should use the blueprint of the 50mm 1.2L to construct the 85mm f/1.4L

- as the 50 1.0 and 85 1.2 are so similar.