There's no need for a "new" Sub-Zero, so to speak. With the new timeline established, I believe that Scorpion/Sub-Zero's rivalry still has to be fleshed out, because MK9 made it come to an abrupt halt when it was getting good, with Sektor and Cyrax ruining everything.
I'll be happy if it's either Bi-Han or Kuai, I'll be disappointed if it's someone new.
I would be disappointed too, but at the same time human Sub-Zero is back, so I'm also happy.
As it is, Cassie Cage worries me about Sonya and Johnny coming back in MK X.
I want to believe they are coming back since they were left alive in MK9 and make sense as the "aged" characters that Boon was talking about, but I dunno.