If FFXIII (360) sells around 2 million WW, I expect a port.
While I'm not going to flat out disagree with you on this I think it would need more than 2 million to make a vsXIII port more likely than not. It would mostly depend on the 360 sales relative to PS3 sales. If 360 is >50% of PS3 (in the multiplat markets) then the likelihood goes up. if 360 sales <50% of PS3 then likelihood diminishes. Absolute sales required to make a 360 port of vsXIII likely? I'd put that more around 3 million+ than 2 million.
I think there will be a good deal of FFXIII sales on 360 that are people why buy to try out the franchise and a decent proportion won't like it enough to be converts to the franchise, so vsXIII has a good chance of selling substantially less on 360 than XIII. Whereas vsXIII is likely to sell as well as or better than XIII on PS3.
If S-E goes all out with vsXIII content then a delayed 360 port could either be a 5-6 disc proposition, or it could end up having content taken out to fit it onto 3 or 4 discs, or even worse it could be reduced in quality to fit on 3 or 4 discs but retain the same quantity of material. Any way it goes it would not go all that well for the 360 port as the "It's identical" statement wouldn't hold up quite as well as it does for XIII. 5-6 Discs would be the best outcome because that way you'll get the same game in both quantity and quality.
And timed exclusivity would be another minus for 360.
There could be some quite serious freaking out by PS3 FF fans if a multiplat announcement was made and it was scheduled for simultaneous release, meaning a delay for PS3, and no doubt meltdowns over accusations that detrimental changes would/will be made to make the porting work out for the 360.
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