Yeah i will wait and make decision wich one to buy after i have handle a E-M5 MarkIII.I'd advise waiting on a decision until you had a chance to hold it and see for yourself if the new material bothers you. Many have said that they couldn't tell the difference, and I imagine it is all a matter of personal perspective. Maybe even wait a while and see how real-life users feel about it after having it for a while.
But i have owned polycarbonate bodys from other manufacturers before so i doubt Olympus E-M5 MarkIII feels much better than the competitors and their own current polycarbonate bodies.
Many have allready said it feels a bit plasticy and current Olympus silver polycarbonate body are not close to same finish and feel of the E-M5 MarkII magnesium alloy body.