For this solution to work, you have to assume that
1. The combining airlines would eliminate every duplication of effort, equipment, and routes. Massive layoffs would have to occur.
2. The low-cost carriers, such as SWA and JetBlue, would not move into those suddenly rationalized markets. And, don't think for a second that major corporations are not making their traveling employees fly on the cheapest available ticket whenever possible. When I was at Texaco in the 80's and 90's we flew full-fare coach domestically so that we would be the first to be upgraded; and, at least business class, internationally. From what I hear from friends still there, that is not the case today.
3. No one will add new capacity. This is the real problem for the future. Boeing and Airbus have not stopped building airplanes. So, for every a/c parked in the desert; a new one (or two) seems to come on line.
You make good points, but IMO, the legacies need to consolidate whether or not your predictions occur (and I believe they will occur).
1. Of course the combined airlines would have to furlough tens of thousands of individuals.
The legacies currently employ far too many people. Too many managers, too many pilots, too many mechanics, too many agents, too many fleet service/rampers and, sadly, too many FAs.
2. B6 and Wn are moving in whether or not the six legacies wisely shrink to three or four. B6 has almost 200 airplanes on firm order. WN keeps ordering more airplanes and will likely have a couple hundred on the way over the next several years.
If you live near IND (a catchement area of over 1.5 million people), for example, there are six different airlines offering First Class service to LAX or SFO or SEA or SAN or, well, you get the picture. You could connect in ORD, CVG, ATL, DFW, STL, DTW, MSP, IAH, DEN, etc. There are simply too many different and duplicative choices. And none of those six are making enough money to pay down their debt and to be able to afford new airplanes.
Sure, more and more companies are requiring purchase of the lowest fare. But that's a gradual shift - AA, UA, CO, DL, NW and US still sell some expensive fares, even some F fares. But none of them sells enough of them.
3. Sure, airlines will add capactiy. Like B6 and WN have been doing since AA last showed an annual profit in the year 2000.
Problem is, the demand for some airlines' products is growing (primarily the products at B6 and WN) and the demand for some other airline products is contracting: Primarily, the demand for F and full Y seats at legacy airlines.
Given that it is almost impossible to shrink to profitability, perhaps those legacies need to grow to profitability by combining and firing the low-paying customers. Imagine a combination of UAL and DAL. They close the SLC and CVG hubs (DEN and ORD substitute quite nicely for them) and UniteDelta fires a substantial percentage of its cheapest fare-paying pax. The resulting airline is only a little bigger than the current UAL yet its revenues would easily be 50% larger.
Sae thing at AA/NW.
So either the legacies combine or they continue to do what they've been doing for over five years: Lose Money and try to beat the losses out of their employees and creditors.