I think they should re-tell the original Sub Zero turning into Noob Saibot story.
Like, in the first third of the game (the part that spans Mortal Kombat 1) Scorpion kills Sub Zero, and then, for the rest of the game, the new Sub Zero comes up and Noob Saibot is revealed somewhere during part 2.

Of course this presents a problem concerning two different Sub Zero characters who cannot be an exact copy of one another, but two different versions of the same essential, and elemental, warrior.

Yeah, but they can't be all in the game.So MK 1 Sub would go.

Or a better idea would be to mix MK 1 Sub and Noob powers.He'll still be Noob Saibot, but with some new powers like black ice or something like that.

Also there are going to happen new events, so the story is flexible and there's no problem for the MK TEAM doin' this.

This has been a topic that's been debated quite extensively. There have been many conclusions, basically in the end these have been the most popular

--CYBORG SUB ZERO--
Wehn Ed mentiuoned a character who wasn't a cyborg before BECOMING a cyborg, a lot of people jumped to the comclusion that one fo the Sub Zeros would be automated in an attempt to change things up. This possibility is generally disliked because it's a slap in the face to people who grew to love Younger Sub Zero over the past 17 years. Despite how much people hate it, it seems to continue popping up.

--EVERYTHING WILL STAY THE SAME--
Self explanitory. My theory is initially this, but instead of STAYING the same, it ends up the same. Different lead up, But Sub Zero is still Sub Zero and Noob is still Noob

It is still unknown if we will even see the Younger Sub-Zero or Noob Saibot at all. I personally hope so. But you never know. We need to wait for more news before we will know anything 100%.

I say "Younger Sub-Zero" because the one we seen at E3 had no eye scar, Unless this is something they plan on changing, I doubt they would leave that out. We will have a stronger focus on the original Darker Sub-Zero at least for a portion of this game if this is a correct final character model.

A lot of people are forgetting that Younger Sub Zero didn't get his scar til MK3.

Also NOT having younger Sub Zero seems stupid. Just because he's not THE Sub Zero doesn't mean he's not there. He's still highly trained in fighting and the cryo arts, and certainly isn't a coward, so if an invasion of Earthrealm were to happen, Sub Zero or not he'd be on the front lines

He diddnt appear with a scar until MK3, but the characters in MK2 are how they looked at the beginning of MK2. I would presume based on MKSM that the events of the scar are actually true, maybe to be changed in where, but I am still under heavy belief that he obtained it During MK2.

I've learned never to learn canon from MKSM, it retcons pretty much every element of the story, it even killed off characters. If it makes it canon in this game there's nothing I can do, but I'm sticking with MK3. By the way, I think they have their MK1 looks because Shang is still old

Personally, while I'm not one of those people who thinks "marked for death" should be taken literally, I WOULD prefer if the scar was a wound he suffered while escaping from the Lin Kuei, rather than during the MK2 tournament. I just think it makes the escape look more desperate and dramatic if Sub-Zero's escape was so narrow, the fight was so close, that not only did Smoke not make it, but he also suffered a wound he'll have to live with for the rest of his life.

By comparison, he wasn't in any important battles in MK2, so there would be no narrative or dramatic connection between the scar and his story if he got it then. The potential drama "how he got the scar" brings would just be wasted. Unless maybe if Scorpion did it, but Scorpion spares the younger Subbie in the end, so that doesn't really fit for me. It would just be anticlimactic.
Not as anticlimactic as Kung Lao randomly doing it for no reason and Subbie not even batting an eyelash afterward, when he SHOULD be all "oh fuck, my face! There's a giant open wound on it!", mind you...but still pretty anticlimactic.

Well, they did it before, kinda, in UMK3. Two Sub-Zeros and Noob.