I really doubt it's XIII. It's a bit unusual for Western gaming publications to call KOF a "huge" fighting franchise. Granted, it is pretty huge world-wide, but in that part of the world, not so much.
Also, it's unlikely XIII would be at E3. Unless an unknown US publisher is handling it, we already know that SNK isn't going. But SNKP has traditionally announced all their games in Japan first, and the rest of the world second. So it would be very, very unusual for another publisher to announce console XIII before SNK does.
It's almost guaranteed to be SCV. (VF5:FS would also be awesome, though.)
When the official XIII console announcement does come, I expect it will be in the pages of Famitsu or Arcadia. In the past few years, SNK has given exclusives to these publications, with online info coming soon afterward. If I remember correctly, news on XII's console release first appeared in Famitsu.
