By my rough estimation, a maxed out 13" MBA fits the bill as a touring music machine. Two USB ports is the minimum for DJs and video artists. Having one on each side makes it easier to fit wide thumb drives and such. No FW is letdown, but an unsurprising one. The Mini Display Port is will be nice for video artists, as long as they have the right combination of $%#& adapters to connect it to a video wall/projector/mixer, etc.
Given how nosy customs agents have become, particularly in this country, a stripped down travel machine that contains a minimum of personal data is a very attractive idea. Say, hypothetically I were to join the Greek psy trance outfit the Predators on a tour of Israel.* The 13" MBA would fit the bill perfectly as a DJ appliance, light duty photo editor, and offer a modicum of Big Brother resistance.
*Something that is never ever ever ever ever ever ever going to happen, but it's a nice idea.