Great ideas; I hadn't thought about the iPad route. That might make the most sense. Am I right that I just need to buy an Apple Camera Connection Kit to do that?
The MX looks beatiful. Almost too beautiful to justify for the rare action it would get, at $500 street. I don't think I could justify fitting it into a suitcase; at that price it deserves its own case and becomes more luggage. (But that is the solution I secretly want anyway.)
Learjeff - what I meant was that if the Nano Piano had both midi-over-USB connectivity (which it doesn't) and could power a controller over the USB connection (which it doesn't) then my search would be over - he'd just plug the module into a small controller, and a small speaker into the sound module. Not that it wouldn't work with DIN midi cables, but would require another power supply for the controller.
The Piaggero is EXACTLY it...perfect, perfect, just at 61 keys won't fit into the train overhead compartments. Just 3" less and it would fit inside (TWISS). But when all is said and done, I may get that for him anyway, and a case he can carry it in right next to his seat. (And then I'll get the MX for me when I travel).