I think it would be like asking who the top player would be in MK9 before it came out. The informed would have either said a top Capcom player or one of the top UMK3 players at the time, or Tom Brady because of his tournament experience and him being top in MKDC. A lot of the people at the time would have (and did) say REO because REO was still dominating tournaments back then in other MK games. Also people said Tom because he had so much time with the game before release, as well as him being a great FG player of course.
So with that in mind, people will probably say the same thing. 16bit apparently has had some time with the game, and is a great MK9 player. REO is good at any FG he's dedicated his time to, so he's a safe bet too. Really ANY top FG player in ANY game is a safe bet. But who would have said 16bit would be one of the top players in MK9 before it came out? What about Maxter, CDjr, Denzell, MIT, Pig, Detroit, Freevolver, Khaotic, etc before MK9 came out, who would have said these guys except people who knew them?
Point is that ANYONE can become a top player in any game they want, ESPECIALLY a brand new game that isn't a "sequel" or new version of another game. Injustice is a completely new game so it's 100% up in the air. Of course top FG players will be better in the beginning. But the game isn't over in the first quarter.