I think it would require a lot of rpgs and other games the Japanese enjoy before the 360 would ever be a contender in Japan. It would likely have to have release schedule much better than the competition. Brand loyalty for Japanese consoles would be a hard thing for Microsoft to overcome.
I'm not too sure about that anymore.
- Microsoft is continually building up their userbase in Japan. It's already more successful than its predecessor by a good margin.
- There is no GT-equivalent game out for the PS3 (discounting GT HD).
- There are more RPGs coming out for the Xbox.
- There are good equivalent software for the Xbox compared to the PS3 (as discussed in another recent thread).
- PS3's sales in Japan are weak (and continually dropping).
Therefore, if Microsoft can continue to release equivalent games before the PS3 does, it's a toss-up as to which console the Japanese will buy (apart from the Wii, that is). I do think it can swing both ways. I mean, looking at the scale of the situation, the PS3 line chart is looking increasingly like the 360's - release a game, you get a spike, which tapers off within 1-2 weeks.
I'm not suggesting that Japan will shift allegiance to the 360, but it hardly seems like the Japanese are continuing their allegiance towards the PS3 either.
Based on the aforementioned factors, I'd say the Japanese market has already sworn allegiance to one console: Their brand loyalty has shifted in favor of the Wii. IMHO, if this trend continues, there will be a battle between the PS3 and 360 for second place in Japan.
Perhaps Forza 2 will provide more insight on this. Can't wait to see the numbers.