I have finally found the dream travel shoe: the Puma Zandy. Looks like a flat (and is) but it's really a sneaker. So comfortable, really easy to take on/off, and perfect for long treks (or even running) through an airport. Also easy to pack/carry around as they are so lightweight. I've also convinced myself the silver color matches everything. They also work as business casual.
Picture from Amazon site, where I ordered it ($55). I've also seen at Nordstrom.