Well after all the conversations here, I found a camera store that actually had the EM-5, the EM-1 and the GX7 in stock and available to play with. They only carry Panasonic lenses at the moment so I played with the 14-42 kit lens for the GX7 and the 8mm fisheye. As a current Canon 40D user, I was impressed by the compactness of all the cameras and lenses, though having said that, I was actually surprised to find that the GX7 was as big and beefy as it was. To make a long story short, they all impressed me. Three observations:
1) EVFs have come a long way. The one on the EM-1 is head and shoulders above the other two. The GX7's, which has gotten good reviews, I found to not be that much better than the EM-5 in practical use, though it is cool that it rotates up and down. One big difference is that the EM viewfinders are 4/3 aspect ratio, whereas the GX7's is 16x9. The Oly viewfinders crop the top and bottom when you switch to video. I think I like the Panny's diopter adjustment better than the teensy little knob on the Olys, though once set, it liklely wouldn't get moved, anyway, and the Panny's is easier to adjust by accident when you move the viewfinder.
2) I found the controls on the EM-1 to be less intuitive to a new user, whereas the EM-5 is a bit more intuitive and the GX7 is setup like what you'd expect from more of a rangefinder style. EM-1 felt to be in a different category of build quality from the EM-5. Panny felt very solid as well.
3) The GX7 has a pop-up flash -- the Oly's don't. They do come with a clip on miniflash but you have to remove two plastic pieces, one for the hotshoe and one for the mini-usb plug. I would probably lose at least one of those two little pieces in about 15 minutes.
BTW -- I did also look at a 70D body. My 40Ds feel more solid, but it seemed OK. Definitely a size difference between it and the M43 cameras.
The next thing will be to see what the housings look like and figure out the cost curve on trying to unload a bunch of Canon lenses (though I will likely keep my 100-400 and a 40D body for any fast action photos). If I do make the switch from Canon to M43, it will be for compactness above all else. Another point -- last year I bought a Sony RX100 and I use it for daily shooting now. But I don't think it would suit me for underwater based on its limited macro ability. In any event, the bottom line for me would be -- is the EM-1 viewfinder $500 better than the one on the EM-5 and GX7, do I really value the pop-up flash, and is there really that much practical diffefence in 2 vs 5 axis IBIS. Everything else is already documented on the review sites.