No use speculating untill we know more. Even if most of the game's content is new, 2 years is a normal development cycle by normal standards, just not current japanese standards. Considering that the tech is already there and the fact that creating a sequel is always easier than starting something from scratch, it really shouldn't blow anyone's mind that they can make the game in 2 years, I guess we're just surprised because we're used to these ridiculous 6 year development cycles.
As for her outfit, I don't think it's outrageous considering what we're used to, at least she doesn't look like she's 12. The damn trailer doesn't give any clues as to where they're going with the story, but I'm willing to bet that out of the entirety of XIII's cast only Light will be playable. The novel seems to indicate that the others will go on with their lives and not be involved with this, Light will probably start alone and make new friends along the way.
As for Versus, I'm seeing a lot of good things in that trailer. Large open areas, the ability to ride mechs and vehicles, both close quarters sword based combat and the ability to shoot enemies from afar in what seems to be mostly real time combat, some cool looking setpieces like that battle on a platform that is flying through the city and a contemporary realistic setting which is a first for the franchise. Not to mention that the game looks really good.