Honestly what all of us rail advocates should be promoting is codifying protections for the National Network. Make it law that trains must run on certain routes as part of the law.
Why? I used to lean towards this position, but have gotten steadily less wedded to it over the past few years. Long distance trains as they exist now, and have existed for the past several decades, seem to me to be fundamentally flawed as a matter of public policy in most areas. What is the justification for long distance trains? Is it to provide basic transportation? If so, how do you justify the difference in service levels? What gives Grand Junction, CO the right to a train and not Green River, WY? Even within a route, the once daily schedules make trains largely irrelevant for about a third of stops--sometimes more in terms of population. An ostensibly national system has broad gaps.
I used to compare it to something like the Coast Guard--despite the fact that there are no coasts in Kansas, say, Kansas taxpayers still fund it as having a safe marine industry is important to the national economy and flow of goods. Even if Kansans have some degrees of separation to the Coast Guard directly, they still benefit by having access to goods imported through the nation's ports. But there is no evidence that long distance trains have any kind of an impact to the national economy in that way. If long distance trains are, as Senator Heinrich says, "vital to the economic well-being of our communities," you would expect to see that reflected statistically. But if you look at the regions of the nation that are growing the fastest, there is no correlation to train service.
If you look at the fastest growing cities in the US, they in fact track mostly opposite to the amount of rail service. Six of the 15 fastest growing cities have no rail service at all in their MSAs. Two more have 3x weekly service. Only three cities (two MSAs) have more than one train a day--and they are 2x daily. Hardly a ringing endorsement of Amtrak in promoting economic growth.
Speaking in terms of publicly funded basic transportation, the only train that fulfills that role over any significant distance is the Empire Builder, where there is no Interstate access for almost the entire route across North Dakota and Montana. Otherwise, with the exception of relatively short segments on the CZ in western CO and eastern UT and the SWC around southern CO, western KS, and most of MO, the routes roughly parallel Interstate highways.
So where do trains make sense? The research has kinda already been done. Rail's advantages of high capacity in a narrow footprint when compared to highway right of ways, but low speed when compared to air travel, lends itself well to journeys of several hundred miles with strong O&D anchors at each end, especially where population growth has constrained highway expansion and increased demand for air travel. Holistically, you would want to promote personal vehicle travel (make 'em self driving if you want it to sound sexier) in outlying areas to a rail corridor that services large cities with frequent service, thus reducing traffic in urban cores and freeing up airspace for long-haul flights that in many cases is being used for short-distance connecting service.
I don't mean to say that long distance trains are incompatible, because much of the east would benefit from a system like that. Northeast to Chicago and southern corridors make perfect sense as long distance trains that can turn over passenger space multiple times across individual markets, eg New York to Richmond, Richmond to Raleigh, Raleigh to Atlanta, to use a hypothetical new train on tracks that already see passenger service.
But the flyover states! you say. The money is all going to those rich people on the NEC! Where is the equality? But the general flow of money in the government is from the coast inwards. There is already huge subsidization of the heartland in the form of highways, agricultural subsidies, health care, etc. These are all paid for by the strength of the megaregions in which mass transit is a major factor in their economic output. As a national policy, to maximize the impact of transportation funding, it should be directed at projects that will serve high passenger numbers in areas where existing infrastructure is constrained.
There is zero reason for the Sunset Limited to exist. At 3x/weekly, it is of no functional use in passenger movement between large cities (one of which it completely misses) and it is paralleled by I-10 the entire distance. You want basic transportation in West Texas? Stick a bus there. Run it daily and it will be more useful than the SL has ever been. Houston, Austin, and DFW are some of the fastest growing regions in the country. Start trying to connect them, fling money at Texas Central if it helps get the project of the ground faster. I have not quite reached Philly Amtrak Fan levels of antipathy towards certain routes, but I'm close.
In an attempt to drag this back to the Southwest Chief, the idea of splitting the route as it has been presented is about the only thing that could make the situation worse. You don't improve equipment utilization, you will almost certainly see ridership drop, and you don't improve transportation options for a single person. If you want to kill the train, do it right, kill the entire thing west of KC, rebuild the rolling stock to a whole pile of coaches, and run as many trains CHI-KC as you possibly can. It's a perfect market, large cities at both ends, maybe a hair longer than the textbook corridor, but there's no direct interstate, so a train would be far and away the most timely form of ground transportation.
Unfortunately, as it stands now, that's legally impossible. The whole transportation system is fundamentally flawed, and at odds with what I would consider good policy in many cases, but I don't think for a second that the answer is to stick our collective head in the ground and run trains the same way we did the better part of a century ago. It's just not good public policy, both in terms of the use of taxpayer dollars and in terms of how to efficiently move people.