I don't want to rain on your parade, but I think UAL has already made a lot of moves along the lines of what you are advocating. Remember the -400s? I have my doubts that we will ever see the -350s we have on order or the 777x. I'm pretty sure the 321-XLRs will be used primarily for TATL routes, replacing larger 757s and 767s and allowing us to serve new markets to boot. Meanwhile, we are still going to need WB aircraft for quite some time on exceptionally long or congested routes. Among U.S. carriers, we should naturally be flying the biggest average gauge aircraft because they allow us to serve the most customers possible within the infrastructure we have to work with.
I have to chuckle at your mention of the Go Forward Plan, not that it wasn't good but because it bears a passing resemblance to Core 4. Also, a long time ago I wrote a paper on Continental's turnaround and became familiar the Go Forward Plan. As I prepared to interview at merged UAL under previous leadership, I went on the corporate website to familiarize myself with the corporate culture at the time. There, I found almost verbatim the Go Forward Plan. A good plan is less important than good leadership. Our leadership right now is much improved. Hopefully I'll still think so in a few months.