Japan: registering vs carnet for new USA Ducati? And taking it back home?
 

Situation: I am an American with a 12 month research contract in Tokyo for Aug 2015 to July 2016. I might or might not stay longer, making one year carnet entry a bit unappealing.

I plan to buy a new Ducati in the US in the next couple weeks. I know permanent import and registration in Japan is generally very expensive but if a bike is bone stock and is a model sold in Japan, would it be cheaper than usually believed? On an expensive motorcycle a couple thousand dollars isn't bad.

Also, I know the US would not allow the bike back as a Japanese export, but how would the US know it was ever registered elsewhere? Could the bike not be registered in two places at once?

Alternatively, if I'm on a one year carnet and will stay longer in Japan, could I just take a road trip outside Japan before it expires, and then come back in on a new carnet?