My roommate plays GM Sub-Zero and while we're probably not the best, I did understand a whole lot about the MU.
First of all, it's definitely NOT at Kitana's favor. The only thing you have going for you is damage--Sub Zero (currently) has to work for his and has to spend bar.
In the corner, you do have to make a hard read. There's no way around it. You can probably gimmick into parry I suppose, but that's extremely risky for 15% payoff (as oppossed to his 30-40%). In this sense, I think Royal Storm is your best bet, as at least you have an air escape option.
Here's what I found useful. Hope it helps:
- Use IAF sparingly. Sub can and will slide on reaction. Even worse, if he spaces you correctly, he can actually slide, not hit you and recover in time for an even better punish. Mid screen is an honest footsie game. Use it here and there to keep him honest and/or if he's full screen, but otherwise, not a good idea.
- You win air to air. You will deal 30-40% plus off a j2 than he will with his. Midscreen, watch out for opportunities of when he jumps, even over your head. Kitana can do a really early NJP, so you will beat out his option at best, get out of the vortex at worst.
- Against GM sub specifically, Float is not a bad idea. Jumping over his head and going for cross-up/non-cross-up means he has to respect your options and not just clone away. You can cancel into float early or late, which does mess up a lot of his inputs. If he's D2 happy, float really high and punish with NJP into 40%. You will outdamage him if he risks going air to air. Long story short, this is how you make him block.
- If you're using Assassin, do not be afraid to react to clone/iceball with EX AS. You don't need to use meter for combo damage--use it to make him afraid to zone you. 19% damage can and will add up.
Good luck.