For what I understand, many people like Rock, because they saw him on CvS2 and thought "Cool!". I admit, he has cool desing and nice theme song, so I wouldn't mind if Rock would appear in KOF-game (that isn't Maximum Impact 2). But I have my doubts, SNK is probably saving him for Garou 2, if that ever happens.
As for this day's trailer, my bets are Ramon, Mature and that South American Girl. And this is going to be short teaser, probably saving longer trailer for Tokyo event.