I was a long-time (and many bodies) m43 user. I'd owned the EM5 for the better part of two years and considered it the pinnacle. When the EM1 came out, I didn't really want one, not seeing much to differentiate it from the EM5. But then I had a chance to shoot with one for a bit and I fell in love with it. There weren't any particular major features that distinguished it from the EM5, but it was one of those "the whole is greater than the sum of it's parts" cameras. Lots and lots of little, sometimes tiny details that they just improved in small ways that added up to a remarkably seamless shooting experience. I can't ever remember what most of them were, having moved on from m43 over a year ago, but I recall just being extremely happy with everything about that camera. I'd love to see it with the new firmware - I'm not a huge user of tracking AF, but now that I've gotten used to how incredibly good DSLR tracking is, I'd love to see a mirrorless camera approach that level of tracking performance...
I'm not in the market for ANYTHING these days, but there's an outside chance I could go back to m43 for a smaller travel system someday. Probably not, because the size of my DF setup isn't a problem in the least, but maybe. And, at least of today's cameras, the EM1 is where I'd start looking. The EM1 with the 12-40, one of the 7-14s, and the Pany 35-100 would be a pretty great travel system. With maybe the 75-300 held in reserve for special occasions. I don't like zooms for every day shooting, but I seem to like them a lot for tourist/scenic shooting...
-Ray