Given that 185s have been running on routes with SP differentials for a while, there's presumably a very good reason why they haven't been done, which makes it very unlikely anything is going to be done soon.
It's also my understanding that only 1 set of differential speeds are permitted over a line, so if you wanted to put some 185 specific speed improvements you'd need to be careful you don't penalise sprinters.
I think the easiest thing to do would be to change the differentials speeds to MU rather than SP, even if you lose a couple of mins from the SP speeds. However the possibility of TPE Class 68 services would make this option problematic for operational flexibility.