MK9 sub zero doesn't have his scar because (if you'll recall... he only received it in the original timeline before he escaped the cyber initiative). In Mk9, this never happened as raiden altered the timeline and allowed sub zero to be cyberized. Hence, no scar.
Now, in MKX (following the new timeline), sub zero does have his scar b/c he received it from Kano prior to whatever happens in MKX's story. So, I believe it is still kuai liang and that revenant sub we saw is him before he somehow gets resurrected.
Sorry Bi Han fans but... Noob be dead bruh.
Edit: I am also calling that Kuai has been corrupted somehow (most likely by being cut by that kamidogu dagger). That's why he doesn't want to help Cassie and co in the first story mode trailer we saw. And why in the Ermac vs Sub intro dialogue, Ermac says, "Your soul is corrupted" and Sub says "Not corrupted, freed"