There's a screenshot of the character select screen? Can you post it here please?

YOumay want to clear your cache, those are Deathstroke and Kano, of course, there;'s also Baraka, Kahn, Darkseid, and Luthor all unreleased, however, if you are saying how after that theres an empty spot, it's probably going to be left empty, or be a render of Dark Kahn. Because the achievement lsit confirms that the unlockable characters are Kahna nd Darkseid
Oh and here's a select screen pic.

There's SUPER UNLOCKABLES.... at least that's what I've heard...

Will all the characters be unlocked besides Kahn and Darkseid or will we have to unlock them too?

Well, that was an early build of the game from Liepzig. As in, it was essentially a demo. The real version and the achievements lsit imply that yes, everyone else will start out unlocked