I disagree that the end of the Wright Amendment has been the primary driver for lower metroplex fares; here is an article discussing the "Spirit Effect" which also applies to Frontier and other ULCCs:
http://www.travelweekly.com/Travel-News/Airline-News/Study-The-Spirit-Effect-lowers-fares-spurs-demand
Spirit is bad news for American and it's bad news for Southwest.
Above, you said that opening up DAL for more gates would allow ULCCs to come to DAL, and then you said that would be a "win-win." I really don't think you mean that, because as a Southwest employee who probably wants higher wages, like most of your colleagues do, lower fares are NOT good. What you want to see are higher fares, which will enable WN to pay you more $$$. If DAL is opened up to more competition, and fares fall even further, you won't get raises. What inevitably happens to airlines with high wages and declining fares? Not something the WN employees ever want to experience.
About WN bringing down metroplex fares: I thought DAL was desirable for all those Dallas-area business people and residents, and if it is, then WN doesn't have to offer bargain-basement fares to attract them, right? Before GK changed Southwest's philosophy of avoiding congested airports like LGA, DCA, BOS, PHL, etc, WN would offer cheap fares to help attract customers to the outlying, less convenient secondary airports WN used instead of the congested slot-controlled airports that it avoided.
Now that WN doesn't have a huge labor cost advantage (nor the legendary fuel hedging advantage of 10-15 years ago), WN can't afford to offer bargain basement fares to attract people to fly its airplanes at the congested convenient airports. For several years now, WN has attracted higher intra-Texas fares from DAL and HOU than AA or UA from their bigger hub airports of DFW and IAH. Intra-Texas, WN is the high fare airline, but that's a good thing, not a bad thing.
Yes, consumers would benefit from even more lower fares at DAL and DFW, but AA and WN would not benefit from lower fares. WN would obviously love to have 64 gates at DAL, but not if it had to share them with any other airline, let alone ULCCs.