a market has to involve two parties. If UA is not willing to lease to DL or any other carrier except WN, then there is no market.
as I have noted before, UA has a lot of reason to see WN grow as large as it can and take as much share from AA since AA and UA have the two legacy carrier hubs in Texas. A weaker AA at DFW provides for more opportunity for UA, esp. given that UA is facing WN's own growth including for int'l flights in Houston.
I don't think it will be too hard for DL to show, if it chooses to do so and I believe they will, that AA, UA, WN, and VX have all cooperated to block DL's access to DAL in order to limit competition.
and whether DL proves that point or not, there is no federal law that requires that a carrier give up its right to serve one airport in a region because it serves another.
except for WN's signature on the 5PA to give up gates at DAL if it starts DFW - a patently anticompetitive measure that serves no purpose other than to keep WN from competing directly with AA.
The clause that requires WN to give up gates at DAL if it serves DFW should be removed from the 5PA and WN should be limited to the 16 gates it had at the date of the end of WA while all remaining gates at DAL should become common use. VX will eventually pull back its operations at DAL because it like every other bidder for the gates has to operate 20 flights/day in order to maintain a presence at DAL, a patently uncompetitive move to limit competition and to force small LCCs to operate economically unviable flights in order to hold onto its gates.
DL is the only airline besides WN that has expressed a willingness to serve DAL and be able to do so with a schedule that can close to filling 2 gates. I suspect in time that DL will end up with 2 gates, WN will have 16 at DAL and as many as they want at DFW, and other carriers will start new service from DAL, splitting the remaining two gates with VX which will reduce its presence to its core LAX and SFO markets.