On int'l flights, you are not allowed to sell flights until you have obtained government approvals but no such requirement exists for domestic flights. There is no legal requirement to obtain government approval to begin domestic service.
There are many markets that have been sold by carriers and never started or terminated before the passenger flies. As long as DL follows procedures to either refund the passenger's money if they don't want to accept DL's reaccommodation, which could easily be done from DFW, there is nothing legally or morally wrong.
And you all can say all you want, but the chances are extraordinarily high that DL will end up with the gates to fly the schedule it has published and may even have space to add more service.
it is also noteworthy that WN didn't announce service to either MSP or DTW, two cities which DL says it would serve.
No one has yet to find a post where I said that DL would definitely file a lawsuit if they didn't get slots at DCA because I didn't say it.
Since the process isn't finished and even after it, legal challenges are still possible.
But I still say that the biggest impact will be to AA who will watch their highest margin hub - by Parker's own statements - become one of the most competitive large markets in the US and one where no US carrier maintains a successful hub against that much low fare competition, and neither AA or US has any hubs with that high of a percentage of low fare carrier activity.
If you're so confident that DL will not get access to DAL, then I am willing to bet you that they will.
If aren't willing to put your belief in your position on the line, then quit making a bunch of noise about it and wait until the process is finished.
BTW, I don't know what Google some people are using but the definition of low fare carrier quickly pops up a number of articles that use the term.