Well, there are four spots remaining, so I can take a wild stab in the dark at a possible four names to be thrown in.
Petey Williams: Yes, he lost to Curry Man, but somehow I see Scott Steiner getting him reinvolved as to not drop him from the list. Plus, how can you not put Petey Williams in a match like this. He has the ability and should be honestly next in line to win that Championship in my eyes.
Sharkboy: I'd much rather not, but he is one of the cornerstones of today's X-Division. I can't believe how sad it is to write that either. Although, Curry Man is in, which means Sharkboy will likely follow since they're something of a team now.
Sonjay Dutt: If you ask my true opinion, you're looking at the possible next X-Division Champion to continue the weird angle with Sonjay and So Cal Val. I'm telling you, its reliving the Savage/Hogan/Liz days. But would Sonjay truly play the part of Hogan?

I can see Val giving congrats to Dutt, then Lethal begins getting jealous.
Kaz: Like it or not, hes still a prime member of the X-Division, and the fact is he'd be a great name to win the Championship. For him, winning the Championship wouldn't be hurtful because the X-Division title is often seen as an equal to the World Championship, depending on how its creatively carried. Therefore, Kaz being involved in this match is a huge possibility, and likely.
Possible Others: I'm not going to say either of the
Motor City MachineGuns couldn't be involved, and in some manner it doesn't look like they're doing anything with them to begin with. However I'm still holding out hope that they could possibly join up with Christian Cage in the Letal Lockdown match.
Obviously if either Gun is entered into this thing, then you'd have to consider
Johnny Devine to be a likely top choice to be entered in as well. Was Devine an X-Division Champion? I know thats almost stupid to ask, because I think he was, but I don't honestly think he ever carried a single match as Champion. I think he won it in a single's match (of sorts) then lost it in a 6 Man Tag Team match. Either way, Devine could be another possibility.
Finally, what about
Elix Skipper? He always seems to surface around this time to play a role in these types of matches. Him and
Low Ki both normally do. However I think Low Ki is gone, technically for good, but I also think hes injured. And I don't know if Skipper is even still around.