#2 Someone who hasn't debuted yet
In terms of stars that haven't debuted with the company, the two biggest names that stick out to me would be Austin Theory, since he's the biggest name currently at the Performance Center, and John Morrison.
Theory was a staple in Evolve and was featured during the tile unification event on the WWE Network. He won the WWN title to go along with the Evolve Championship. Theory was also shown in the stands at TakeOver: Toronto in August. Since his signing, the former dual Champ has been performing at NXT house shows. Could his debut with the yellow and black brand be saved for a huge event? Or is his time on NXT proper still a ways away?
In terms of Morrison, he has no ties to NXT but has reportedly signed a new deal with WWE. That was almost two months ago, but nothing has come from it. While I think he should and might be going right to the main roster, it wouldn't be out of the realm of possibility if he returned in grandiose fashion at WarGames.
If he did show up, he'd immediately be received as a face. He's also a Parkour master and that's something that would play well into the WarGames structure. One of our own star analysts, Gary Cassidy, also has some feelings regarding a possible Morrison appearance at WarGames.