I thought about pocket doors too, and came up against the same questions you have. If the door is sliding across the [long axis of the] bus, there really isn't a way to get around the curve of the ceiling and how it limits the height of the door. For the tracks being visible, I thought that the use of drawer slides within the wall (and attached to the door near the top & bottom) would keep the tracks out of sight, or at least off the floor & ceiling.
Another option is an accordion door, which personally I don't care for. We only have one door in the bus (bathroom) so I was able to nearly sidestep the issue completely!