So you know of Mileena and Havik but haven't heard of Rambo? Well, unless you know all the characters (and you yourself are saying there's a KP3! 3 would mean at least 8 more, right??) then I believe that you may have some info just like the other "leakers". One may know about Mileena, one may know about Havik, one may know about others.
They seem to correlate on there being 8-9 more characters, with Havik, Daegon and Quan Chi in it+ at least one more guest. One mentions Mileena too and she was on that leak with Shinnok from before the game released 1 year ago. You say you know something about Mileena too. Those should be 5 characters out of the 8-9.
For the rest, we can exclude the ninjas who appear as part of Shang Tsung's gameplay and Cyrax and Sektor after Robocop's appearance.
So who is left? Who could be playable? Well, there's Takeda, Kung Jin, Ashrah, Reiko, Sareena, , one leak says Taven, Shinnok, another says Kai, John Wick and Deathstroke. It's got to be out of those. I can;t see anyone else. Some were DLC in previous games. Can't see Nitara being in with Skarlet there. Can't see any of the ones who died in the MKX comic: Mavado, Hsu Hao, Drahmin (sadly), Moloch, Kintaro. Onaga will surely not be now. Really don;t see Chameleon, Darrius, Dairou, Meat, Mokap, Kobra, Kira.
So that just leaves as potentials Takeda, Kung Jin, Ashrah, Reiko, Sareena, Taven, Shinnok, Kai, John Wick, Deathstroke and let's say Stryker for 3-4 roster spots, with nothing heard about Kung Jin.