First of all, congrats to Markos for scoring the tasty Newsweek opinion gig!
His announcement, though, intriguingly offers this little nugget:
But Newsweek is "balancing" me out with someone that should make heads on our side explode. Announcement on that name is still a couple of days off.
The way this is worded, I'm guessing Markos knows who his Republican counterpart will be, but isn't allowed to say. (I'm also guessing that Kos wouldn't agree until he knew who the other side would be, as well, to assure he was pitted against someone of equal stature.)
I came up with the following names, of which I think Michelle or Ann would be the most likely (having a woman on the "other side" seems demographically useful, especially with the potential added tension of a Hillary nomination.) Someone like O'Reilly would seem less likely to me (since I doubt Bill would "lower himself" to Kos), but might be possible from a fireworks perspective. Either way, let me know what you think of the following list, and if I missed a likely person, mention them in the comments!