I think I'll up what duckroll is saying and say Is there a single console in Japan with a better Japanese-orientated lineup in December than X360?. The PS2 has dried out mainly, the PS3 hasn't started, the Wii schedule is empty post-launch, and meanwhile the X360 has non-stop games for Japanese folk.
If X360 systems start moving, the software (Culdcept, [EM], etc, etc...) that's aimed at Japanese buyers will start moving as well. This would cause 3rd party developers to say "Hey, the X360 seems like the best place to make games that actually RETURN PROFIT" and to start working on and announce new Japanese beloved franchises for the system.
This in turn causes more people to buy X360 hardware for these new Japanese games, which in turn causes older software to sell more, which in turn causes new games to be announced, repeat.
This is the ball and how it rolls. IF (note this might not happen. Right now it's a complete gamble that no one has any idea if it'll pay off) it starts rolling the momentum would put the X360 into an ever moving chain of events to sustain it as the #1 console for Japanese gamers this gen. When the DS ball got rolling it was unstoppable. The X360 has a chance to do that and that chance is DECEMBER.
DECEMBER will either SAVE the X360 for the next 5 years or DESTROY IT as a total failure.
If I was a betting man I wouldn't bet either way because it's just too damn close.