I think the problem is that most of the other JL actors are tied up. Alan Ritchson is doing Blue Mountain State, Lee Thompson Young was on FlashForward until recently, and Kyle Gallner's on CSI: NY, and doing the new Nightmare on Elm Street. And Alaina Huffman's a regular on Stargate Universe.
My guess would be that they'll bring Cyborg in for the finale this year, unless Young gets another gig: his schedule is pretty clear now. Add in three or four of Shanks, Irvin, and Morris, and maybe Ritchson, for the big Apocalypse, and we'll see what happens.