I'm a latecomer to this discussion, but I've enjoyed getting up-to-speed.

Disclaimer: I've never worked for an airline (though wouldn't mind doing so), though I fly a lot and I conduct research on marketing and human decision-making.

In theory, I like the E+ idea that a bunch of people have mentioned. In reality, I am skeptical of its ability to raise the necessary revenue system-wide, and I'm concerned about the up-front investment costs to re-do all the domestic cabins. But, in the spirit of this idea, would it not be possible for CO to change the front part of the coach cabin to look like (though not be identical to) intra-European business class?

I'm not talking about removing seats and increasing pitch. Instead, I'm talking about very explicitly blocking off middle seats to guarantee that some people have more room. But, not just that--also having the ability to block off middle seats in more/fewer rows depending upon the route and overall demand for seats. This would create a certain variety of domestic E+ experience (more horizontal space, yet equal pitch) without the extensive initial investment, and also with the flexibility to change the size of the E+ cabin as needed for certain routes/times of day. Maybe some routes at certain times of day just get 1 row like this, whereas others get 7.

The key, though, is that they could market an E+ experience, and potentially generate a revenue premium from it, but not incur the large investment costs up-front AND be able to make route-specific adjustments to the size of this "cabin". Unlike with AA's MRTC, it really wouldn't matter as much if there are certain routes for which they know that demand for more room is low.

For me, at least, if I can't get an upgrade, the next best thing is having the seat next to me free in coach.