I personally think... the (Dallas) Fort Worth Airport should be the North End terminus. Let all the other rail + Taxi + Car traffic merge at the DFW Airport.
If I were investing in Texas Central, I wouldn't want to spend the money to enter downtown Dallas and spend more money to also leave downtown Dallas just to get to DFW Airport. Golly, Texas Central and the FRA have already balked at spending the money to get to downtown Houston, imagine whatshock they'll experience if someone tacked on additional costs getting out of downtown Houston, to go to Hobby, Bush International, or even Galveston?
How many HSR passengers boarding the train in Houston will want to go to DFW Airport, when Houston already has two airports? How many HSR passengers boarding in downtown Dallas will want to go to DFW Airport when they can ride the Orange Line with much, much, much cheaper fares? Therefore, I believe it is safe to suggest about the only HSR passengers that might want to go to DFW Airport will board the HSR train in College Station, which by the way will be located a good 15 to 20 miles away from that city.
What transit advantage will a DFW HSR station have over downtown Dallas, if any? One will be able to walk a few blocks from the downtown HSR station to reach both TRE trains towards the mid cities and downtown Fort Worth. One will be able to walk a few blocks from the downtown HSR station to reach both Red and Blue lines towards Oak Cliff, Richardson, Garland, and Plano, or connect to Green and Orange lines to Carrolton, Farmers Branch, Irving, Pleasant Grove, and DFW Airport.
From a DFW Airport HSR station located on its south side, all you'll be able to catch from it, or be within walking distance, is the DFW Airport People Mover! Then it would be just as long a walk from the People Mover Station to either the DART station outside Terminal A, or the TexRail station outside Terminal B.
I fail to see any transit connections advantages at DFW Airport for Texas Central's customers.