I'll be honest — if I knew a photographer were going to shoot my project on an m4/3 camera, I wouldn't hire him. If i found out afterward, I wouldn't re-hire him.
Obviously, matters are different for the 'journalism' field, if you're shooting for web, or still shooting for newsprint. But, as an AD, i'd really look elsewhere, toward a photographer who seemed to demonstrate more commitment to the craft. Still speaking honestly here: yes, i have a prejudice. Against small format digital. And, more importantly, against photographers who are now choosing gear based on size/weight. I don't feel it's a significant burden to carry/use, at minimum, an APS-C sensored camera system. And, since size/weight seems to be the only advantage of an EM5-OMD over something I consider 'more serious,' I really feel photographers are getting lazy and taking too much for granted.
Don't forget that a lot of ADs and editors are also photographers. Your gear ought to be better than his. Or, different for a demonstrable reason. ADs and Editors also consume visuals. They are connected to a good number of photographers. They have other options.
Yes, I'm an old (fuddy-duddy)school dude of 45 years of age.
Besides that, using the small sensor cameras too often results in pictures that look like they came out of camera phones. All DOF. Not an aesthetic i'm particularly fond of, but more than that, there's the suggestion that i'm not going to get any variety in that respect. And, ADs/Editors tend to like choice.
Personally, i think you can 'get away with it' if you're not working alongside an editor/AD, and you really blow him away with the images. But, if you're not a spectacular photographer, you're giving away the sense of professionalism and potential. As has so often been said in advertising, you don't sell the steak, you sell the sizzle. And, an OMD has ZERO sizzle. I'm not sure why photographers don't have the sense that they are always marketing themselves.
It's rare that a guy like Terry Richardson comes along — someone who does professional, high-end, high-budget shoots with a $300 point and shoot film camera. That was akin to gimmickry. A magic trick or a hoax, depending on your perspective. But, Terry Richardson was already a 'name,' and his gear contributed to an aesthetic. That's not common. Lightning in a bottle. If you're trying to shoot editorial travel, you're going up against Canon 5DMkII and IIIs and Mamiya 7s.