I still believe they have Kombat Pack 2 up their sleeves and mostly due to the fact on the fate of one fighter who was supposed to be in Kombat Pack 1 but was replaced by The Joker. Below is whom I believe and why they would be in KP2 if it really takes form. Keeping with the 6 fighter limit tradition.
1. Ash Williams -- the Evil Dead hero was slated to be in KP1 and even some pre-order screen shots of the advertisement to order KP1 has his name along with the other 5 we have gotten. A lot of people believe The Joker took his place in KP1 and I have to agree with that but I believe he'll be available in KP2.
2. Michael Myers -- with the inevitable Halloween Kills due out this October it makes sense to release him finally in a pack to commemorate his new film. They did the same thing with The Terminator seeing how Terminator had a new film and with Michael Myers having a new film it seems almost a done deal.
3. Mileena -- say what you will Mileena is still a high probability. Fans are asking for her all the time and her MKX ending still makes it possible for her to survive her fate from the MKX story. I believe Boon even teased her once on his Twitter feed. It also feels so odd to have Kitana and Jade and not Mileena.
4. Havik -- I don't personally like Havik at all but there is a lot of speculation that he'll wind up in KP2. A lot of fighters reference him in their dialogues and some in their endings. I'm not too sure where he'll fit within the story but he is a high probability as well.
5. Tri-Borg -- even though Sektor and Cyrax are already in the game, simply Tri-Borg colored different, I have a feeling Tri-Borg will be back with all the abilities he had in MKX, and of course his multiple skins and colors could be customized to make a Sektor, Cyrax, etc. cyborg ninja. He may even be given Hydro's powers seen in the fan games too, there is a Hydro Konsumable. LOL. But in reality either Tri-Borg or both Sektor and Cyrax.
6. New MK Fighter -- depending on if Sektor and Cyrax would take the last two slots or not depends on the last character to be introduced to MK11. We've only had 3 character introduced in MK11 so the last choice I think we'll see another new fighter enter MK11 that we've not met yet. I personally think it would be an awesome idea to bring back Bi Han from MK1 since we now have a time traveling story arch where almost anything is possible. Just to see him interact with his brother as Bi Han before he died would be cool.