Well..
It´s safe to say that there will be no Halo3 anytime soon. If there is a Halo3, expect the "critical" holiday 2007.
One "dream-scenario" (not that I dream about it..
) for MS is Halo3 AND GTA:Tokyo for the holidays of that year...
Wait a minute... wtf is GTA:Tokyo??
Hehehe.. this is me speculating. I think that MS would want to secure "as much AAA-games" exclusivly as possible for Xenon. MS can "counter" anything Sony has to offer, at least some of the great titles...
Sony got Gran Turismo = MS has Project Gotham, Rallisport and hopefully they can establish Forza as a franchaise
Sony got GTA = I believe that MS will not let Sony make some deals with Rockstar. I expect MS either buying Rockstar or giving away moneyhats for securing GTA for Xenon (and PC)... and probably make something happen there between Xenon and PC-version thanks to XNA. By buying Rockstar and letting them develop a GTA based in Japan (Tokyo) could attract more gamers in just Japan and could be the biggest selling western game in Japan, hopefully making some great impact over there, helping Xenon out.
Sony has great Japan-support and some RPGs from SquareEnix = Square is bound to look at Xenon sooner or later. Xenon will increase in marketshare and SquareEnix cannot overlook it. I expect some SquareEnix games being released for both PS3 and Xenon, to cover as much costs as possible.
Both Sony and MS has great thirdparty support. Sure, Sony has the edge, but the majority of the biggest 3rd party titles comes out on both machines. Xbox has the edge with PC-games though and Xenon will probably continue this legacy.
MS, I believe, has some chances of fixing the Japan-situation. It boils down to "bombarding the japanese" (no offense) with established franchaises. MS has failed miserably with Xbox in Japan because the lack of huge franchaises are missing or coming out later... and the whole design also has some contributions... and the fact that it is an american corp... and so on. But this is fixable, MS will have to invest money in developing games based on huge franchaise. I think its better for MS to do it themselves because if the game succeeds, it will give lots of cred to the inhouse-team in Japan. So the next game coming from them, maybe isn´t based on a huge IP, but gamers will be interested because it comes from the inhouse team that brought them [very-popular-game-based-on-a-huge-franchaise].
well...
just some thoughts...