The only two that I think are likely to be released are JTG and Tyler Reks. They have had their chance but haven't been able to get over. Out of the Divas I would release Rosa Mendes and Alicia Fox, WWE have enough Divas and they are the bottom in my opinion.
I'd be surprised if Tyler Reks isn't released as we don't even see him on Superstars anymore. It sucks as he is good in the ring and has a decent gimmick, yet he gets given zero. As for JTG, his size has mainly been his downfall, but I'd be surprised if he is kept too.
I actually don't see Alicia Fox being released as she wins about half her matches (when she actually appears), but Rosa Mendes really shouldn't be kept.
I do see a lot of releases from wrestlers that were part of NXT and haven't made it onto the RAW roster. Eli Cottonwood, Lucky Cannon, Derrick Bateman and Conor O'Brian are the first names that come to mind.
First off, Cottonwood should be released for sure. He failed miserably on NXT and was the only past Rookie that wasn't included on Redemption that either wasn't on RAW or Smackdown, or was wrestling dark matches.
I hope Bateman isn't released, he shouldn't be anyway. He has tons of charisma, is great on the mic and he was basically the only NXT Rookie in the show's history that actually got the crowd behind him. That proves something.
Cannon and O'Brian won't be released at least until they're eliminated form NXT (unless one of them wins it, which I doubt). Cannon at least has a gimmick and was the FCW Champion until just after NXT started, so they must see something in him. I don't hold much hope for O'Brian once he goes on his own, but then again I thought he'd be eliminated after Novak yet he has actually been decent.
Anyway, I think those on the main roster that would be on the bubble would be Chris Masters, Curt Hawkins, David Hart Smith, Goldust, JTG, Primo and Tyler Reks. I reckon Ryder would be there if it wasn't for his popularity. SUrprisingly that list are all RAW superstars.
EDIT: As if they've done jack shit with Rollins. He'll surely be on NXT6.