Jason Todd is my personal favourite theory.
if they didn't reveal maybe it was no one. they just had thought of no one for the job and made a whole new character, the whole mistery thing was only for thw show, not really meant to be a great mistery, otherwise it would have been answered or more obvious to answer
Red X is either an android, a clone/man-made human, (an altered) Jason Todd, or a Dick Grayson from an alternate-dimension.
If none of these theories are right, well I'll truly be damned.
Hopefully if/when we find out Red X's true identity, DC's theory will make sense. And one of my wishes before I die will be granted.
Uh oh.. Red Hood, Red X.
Mad h2h skills.
Once could've been a hero.
Works selfishly for only himself, to further his own interests.
And Red X doesn't show up anymore.. But Red Hood does make a lot more appearances now.
And Beast Boy has mentioned Jason multiple times when bringing up Red X.
I'll jump on the bandwagon and call him Jason Todd. Perhaps while Grayson was Robin with the Titans, Bats got Jason, that ended well, Jason came back prematurely aged by his time in the Lazarus Pits, and thus calls Grayson kid.
Personally, I think he may in fact be Jason Todd. Think about it: It was said that only a Titan could have gotten into the Tower, and we don't really know how much time passes between each episode, so Jason could have been a Titan like the comics. His violent skills and vigilante status attributes to Jason's Red Hood persona (Red X....Red Hood?) Red X even addresses Robin when asked about not being a hero, saying, "Doesn't mean I don't know how to play one." And Jason Todd IS shown on Beast Boy's chalkboard, when he lists the possibilities as to who Red X is. I think that Red X is in fact Jason Todd.
( From a different thread ^ )
These theories are starting to make more sense to me now. ^
For now, I think it's Jason. Though I don't think they're going to reveal who Red X is anytime soon though.. But let's be optimistic.