I noticed that both big Asian 'import stores', Lik-Sang and Play-Asia, received their Japanese Xbox 360 stock and still have them in stock at time of writing.
If you consider buying this (at ~440usd they are cheaper than on ebay) you should know:
* It'll play only NTSC/J and not-region-coded games (play-asia reports that the 4 Japanese games they could test so far are all region coded, but 7 of the US games are NOT region coded)
* It's 110V (same as US, but 220V countries (Europe,...) will need a stepdown adapter with at least 250~300 Watts power output according to lik-sang)
* There's no exchange warranty service
There's no core/premium choice in Japan, only the 'Commemoration Pack' selling for 37,900yen (today that's ~314usd or ~266eur) without taxes. It's basicly the same as the Premium pack in US/EU, but cheaper, with a Final Fantasy XI beta demo disc (playable) and the video cable is a d-terminal high-definition cable.

btw the remote control is different from the one out europe cause i seen it in stores and it was much larger......and the windows logo was in the middle of the control.....