Here's a few bits of knowledge most advocates completely are unaware of when proposing additional services on Amtrak, either regional trains requiring state subsidy to cover Amtrak's losses, or long distance trains that Amtrak subsidizes all by itself. First fact, that dividing line between long distance and regional trains is by law defined at 750 miles.
Second, how many trains it takes to provide the additional services. Take the Heartland Flyers as an example. It requires one train set, leaving OKC early in the am, arriving FW around noon, all maintenance and cleaning done in FW, leaving FW in the early pm, arriving in OKC prior to midnight.
One train set works. Extend that train to Newton, Kansas one train set still works with very early arrival and immediate departure in the wee hours every morning (3-4 am). Do you really believe Kansas will subsidize a train at that time of day? So, in reality, for an acceptable am departure from Kansas to an acceptable pm arrival to Kansas, two train sets will be needed. That's 2 more locomotives for bi-directional running and at a minimum 2 more Superliner cars.
The Texas Eagle uses 4 train sets because the south and north bound trains meet twice every day. Every time they meet, there are two trains on the tracks. They are scheduled to meet in Fort Worth and to just miss one another near Chicago, arriving in Chicago at 1:44 pm, and departing Chicago at 1:52 pm. There is no way they can reuse the same train in Chicago with just an 8 minute stop and turn around. So, four train sets are needed to run the Texas Eagle. It is so easy to fall with the misinformed belief the Texas Eagle requires just one train set.
Third, what does Amtrak need to maintain and operate the trains. Crew experienced on the right of way to operate the trains safely. Crew trained to service its customers (passengers) both aboard the trains and at stations when necessary. Crews to maintain the trains in a shop area. The maintenance shops and yards. Vendors supplying the goods needed to service both the trains and its passengers. Take for example a second frequency between Dallas and San Antonio following the existing route. It would require an additional Superliner train set at a minimum, and most likely two Superliner train sets for mostly daylight operations. Amtrak would have to increase maintenance crew in both Dallas and San Antonio and its operations crew on the trains. And Texas would have to subsidize Amtrak's losses because the route would be less than 750 miles in length.
There are advocates today led by the mayors of Austin and San Antonio for someone (Mexico,Texas, and/or Amtrak) to run more intercity trains between them. To eliminate them from funding the project, they have changed the terminating stations north to Fort Worth and south to Monterrey to make the corridor length more than 750 miles, and if needed north to Oklahoma City if Fort Worth does not get the Texas subsidy guarantee. The longer they make the corridor, and the higher frequency of trains ran, the more train sets will be needed, along with more crew of every possible type. Can it be done? Will it be done? Who ultimately will pay for it?