If there's no Grunt costume in the mix, I'm gonna be disappointed.
According to Andriasang, the latest issue of Famitsu revealed that Square Enix is partnering with BioWare/EA to release a DLC costume pack for Sera and Noel based on Mass Effect 3's "main characters." Presumably the this means the Normandy crew. There's no word on whether this costume pack will have any other effect on the characters besides a cosmetic one or if Square Enix might be returning the favor with FF costumes popping up in Mass Effect 3 (this would be unlikely).
Both Final Fantasy XIII-2 and Mass Effect 3 are available now.