As I said before, the truly great will succeed no matter what and the truly bad will fail no matter what. I'm concerned about the "late bloomers." I want a system in place that will help them realize their potential. There are plenty of authors who are now considered iconic, who had very rough starts and only realized their potential because someone in the publishing industry spent a lot of time and money helping them develop. Frank Herbert is a prime example of this. Despite all of the mentoring he got from experienced editors, he certainly broke a lot of new ground, so I'm really not all that concerned that "unleashing experienced editors on new authors probably reduces variability in writing." Mentoring is all about helping other people develop, and part of being a good mentor is understanding that you're there to facilitate growth, not direct it. We might get a little bit more uniformity from having editors mentor new writers, but I think that's far better than losing great works because they are never written when new authors have no choice but to jump right in to the sink-or-swim world of self-publishing.

Consider an author who has great potential, who will, given enough development, write bestselling novels. Unfortunately, he's still too inexperienced and his current work could be described at best as mediocre.
If he tries to self-publish, his books will be (rightfully) criticized as being not worth reading. He will not make any money, and will likely be forced to give up writing and take up another profession. If he is especially persistent he might try again, but without a mentor his skills won't improve very quickly, and even if they did he still has to fight against his well-earned reputation as a second-rate hack.
On the other hand, if he sends his work to a traditional publisher, there is a chance that someone will see the potential in his work, pay him for the book, and work with him to improve it to the point where people will want to read it. Then he'll get a crack at a second book, and the help he needs to make it better than his first. In this way, he has a chance to grow into a truly great author.

As long as there are publishers who are able to successfully identify and develop such diamonds in the rough, and unless someone comes up with a different way to perform this task, the traditional publishers will not go away. Even if they lose all of the authors who are good enough to jump right into self-publishing, that still leaves them with a significant role in the market, growing great authors.

I strongly suggest that you check out Baen's Universe: all of the issues are electronic and DRM free, and since publication has ceased, you can buy every issue ever for $30 (+ $6 for the very last issue). Every issue has at least one (usually more) article about the publishing industry, usually focused on copyright and DRM. The first issue includes an article explaining why the magazine was started, and it was to provide exactly the sort of development opportunities to new authors that I've been talking about here:
http://www.baens-universe.com/articles/editorial_one
The last issue includes an article explaining why publication was ended (in short, the magazine had served its purpose):
http://www.baens-universe.com/articles/So_Long__and_Thanks_F...