Likely, CO's thinking is that they've now given us SWU's, although not at the same number as UA, the MM program and some other items to keep people flying CO after reaching whatever Elite level was wanted, therefore coach seating, which has been a bane of existence for all of us for years, won't be changed anytime soon. I remember when we were told at the first DO's that CO was looking into changing Y seating to the rocking shell seats, or something else more comfortable; but by DO III, that line was over, despite the groans. Remember how long it took CO to step up to lie-flat seating in BF? They could no longer use the "We're waiting for the 787 to arrive" excuse after doing so through about 3 or 4 delays of that plane.

Personally, I really liked my time in E+ on the UA flights I've had. I'd really like to see it at CO. Failing that, comfy shell seating all around would work for me. I don't know the cost/weight/load factor of one vs. the other, but E+ was a very, very positive enhancement to me. And I paid for it.