I'm still not sure how to take this revelation.
Noob Saibot is one of my favorites. And I always liked the original Sub-Zero. More than the current one actually. And this twist could lead to some interesting plots involving Scorpion, Sub-Zero, and Sareena.
But on the other hand, I'm not really keen on "x was really y this whole time" twists.
Guess the pros outweigh the cons.

It's a very interesting twist, and could explain why Noob chose Smoke as his protege or whatever since they were both Lin Kuei. My question is which Sub-Zero was Noob Saibot? In the ending it says he was the original Sub-Zero meaning Sub-Zero 1, whereas the current Sub-Zero and the Sub-Zero in MK1 are like Sub-Zeros 4 and 5. I'm guessing that he was the Sub-Zero in MK1 since they did mention that he was killed by Scorpion. I wonder what kind of story they could now make with Shinnok, Quan Chi, Sareena, etc now that we know Noob is Sub's older brother.
....or maybe it's a Deception and just a "What If?" but I hope not.

Yeah, they mean the Sub-Zero from Mythologies and MK1. That Sub-Zero is also sometimes referred to as Sub-Zero 5, but it's the same one.

It seems Sub-Zero was so in love with Sareena, that when she couldn't leave the Netherrealm with him, he somehow managed to join her in the Netherrealm.
Ka-Tra