It is too bad that the stop can't be at Union Station, or does "near" mean possibly at the other end of the platform? That is probably wishful thinking on my part. Union Station has tons of transportation links, Amtrak of course, cafes nearby, security plus some sort of waiting room I would imagine. Union Station is the downtown stop that Houston wishes it could have. I have read that the Texas Central Dallas stop is going to be in the Cedars, but that is a fairly large area.
Is the Dallas stop going to be on the Amtrak "mainline", on the Dart Red/Blue Line, or is it going to have its own right of way? Sorry for the basic question but I haven't read which it is going to be,
The Dallas station is expected to be near Union Station, so it would be expected for a connector to transition the 1/4 - 1/3 mile separation. In Houston, being at the I-10/610 intersection, a bus connector would be required to get to downtown Houston.
It appears that this train plans to be separate from other transportation, like those that find a better deal to fly in the other city, they still have the issue of getting to the airport.