Full Frame and mirrorless don't go together. An 85mm lens on an APS-C and a 135mm lens on FF have the same Field Of View. One of the BIG selling points of mirrorless is small & light. Hanging a BIGGER FF lens on a smaller mirrorless body kills that advantage.
I should point out that a 135 f/2 FF lens designed from scratch for an EVIL FF camera can be relatively small and lightweight due to the shortened flange distance.
Personally, I will never purchase a mirrorless camera, having used one for a year. The conclusion I arrived at after one year of trial is this: I HATE EVF.