Orion is designed to support only one EVA. There's no airlock so the entire spacecraft would be evacuated of air during the space walk and then repressurized from gas flasks, with a storage enough for doing it only once. This might be sufficient for current ambitions for HSF, but could it be upgraded to do several EVA's? And what about Dragon v2 and CST-100, are they designed for any EVA capability?
I imagine that the service module could be extended to allow for gas storage for multiple pressurizing events. But couldn't one also attach an inflatable airlock so that the entire spacecraft does not have to be evacuated of air? That's actually how the first space walk ever was done, by Alexey Leonov in 1964 as illustrated below. Today maybe a suitport would be a better idea because Alexey had quite some problems getting back into that rubber bag. (Maybe a couple of suitports should be put on the ISS just because it's simpler than airlocks?)