Prediction (with no basis in fact): They will try to do this very simply with a set of ability ranges by level/xp. You will either use them directly and read a range of allowed monster attacks, hitpoints and damage from a table, or you'll build the monster from components and eyeball where it falls into the table to decide level/xp.
hmm....this brings up another issue I've thought of before: Monsters vs. "people". That is, should the rules be different for creating something with the incorrect number and type of limbs that roars, bites, claws and other untoward things and for creating something that has a basically humanoid form and could learn things like humans do?
Second prediction (with even less basis in fact): It will kind of work, but won't be perfect. Not as tight as 4E's designated values, but not as loose as 3E's CR system.
I think I'd be generally OK with that (depending on what "won't be perfect" means. I think there's a limit to how accurate or precisely any such system can be (from either direction) and worrying about nailing it exactly from any direction is likely an exercise in futility.