EF 85 1.2 MK II is already an awesome lens, than why should canon replace this one with mk iii so soon. There should be a reason to update the lens. Some people saying it is a slow focus lens, yes it is bit slow compared to other L glass but there is reason behind it : 1. it is 1.2 lens, at 85 mm with f1.2 depth of field is so shallow, to get the best accuracy for focus canon made it bit slow. 2. this lens have lot of glass inside and whole front optics move to focus the lens that is why this lens focus by wired to provide enough power to move the whole big chunk of glass. apart from bit slow focus this is an awesome lens and keep in mind this is a portrait lens and portrait lens does required to be very fast. Thats why too many other lenses are available to capture fast subjects. If you need best picture quality form a portrait lens go for it, you won't be disappointing.
EOS 1DX, EOS M with EF 35 1.4 L, EF 40 2.8, EF 50 1.4, EF 85 1.2 II L, EF 100 2.8 L IS, EF 135 2 L, EF 300 4 L IS, EF 24-70 2.8 II L, EF 70-200 2.8 II L IS, EF 2x III, EF 25mm, EF-M 18-55 IS, EF-M 22, 600 EX -RT, 270 EX II, EX 90