I seriously don't want a "challenge rating" system in D&D Next.
Here's why:
Challenge is arbitrary.
A group of skilled players and a group of newbs might both go up against the same "challenge rated" encounter, and the newbs get TPK'd and the veterans mop up the floor.
But, crap, these CRs are mathematically balanced for 5 PCs, but I'm running 7 or 3... Now I have to adjust on the fly anyways.
Or, the way you run kobolds and the way I run kobolds might be completely different. You keep them bunched up in a line with no ranged weapons so they all get cleaved or burning hands'd to death while I use clever tactics and ranged weapons and cover.
In other words, these XP values correlating to challenge are basically a waste of time.
Instead, I'd rather have "treasure" values. Certain creatures are naturally tougher of course. No one will argue that. But, as a DM, I don't have to worry about perfectly balancing every single encounter to my veterans of 7 PCs or my newbs of 3 PCs. What I do instead is develop an environment with the appropriate rewards for the monster.
An ogre has 300gp while a kobold has 1gp.
Then, it's up to the players to choose their challenge. Not me. They can go after the kobold chieftain with 50gp or the ogre with 300gp. Is it going to be a fair fight for them? That's up to them, isn't it?
Maybe they go try to fight the ogre at a lower level and risk death for the extra gold? Maybe they decide it's not worth it and pick off the kobolds instead. Maybe sometimes those hard monsters don't carry treasure. So, instead, the players avoid them at all costs.
This is the kind of play I'd like to see. The players learn quickly that sometimes you run because it's not "balanced" to them perfectly. And, the dice fall where they may.
If you want to prevent TPKs, give players clear indications of a creature's power level (a big treasure hoard is one...) and let the players decide whether to risk it or not. And, also provide rules for fleeing that allow the players to make that choice and live to fight another day.