I'm sure they are planning to include UNIQUE returning characters, despite of some of them being dead. I'ts MK. All characters have been dead at least once in the past anyway.
The 3 variations system pushes imagination and design to the limit, so they can't and don't need to include generic fireball shooters. Characters like Noob Saibot, Cyrax, Kitana, Ermac, are more "special" thus, opening doors for inspired move sets and overall variation designs.
That's why there's no chance you're seeing Frost. Sub-zero already covers whatever an Ice warrior can be.