Denver-Colorado Springs-Pueblo might be a market for a viable corridor, with a possible extension to Albequerque, but....

The "but" is that the Joint Line is single track through Colorado Springs. In the early 70s, shortly before the Powder River coal traffic took off, the Santa Fe line was abandoned from Palmer Lake to just south of Colorado Springs. All traffic now uses the former Rio Grande (UP) line through Colorado Springs, and, with the amount of coal traffic on that line, it is a bottleneck. Trying to add 79 MPH passenger trains to the mix of 40-50 MPH coal trains would make it even worse.

Much as I'd like to see Amtrak expand its service (and I've seen models that show that having 3 or 4 trains per day on long distance routes with a network of trains, so you could make connections), the railroad infrastructure needs to be there for it to happen.

California has spent a lot of state money to upgrade lines that California Amtrak trains use. If Colorado wants to have more rail passenger service than the CZ, it will probably need to cough up some money to put the double track back in on the Joint Line. From there, state sponsored trains south from Denver would become practical and possible.

Too often people think of long distance passenger trains as just serving their end point cities, and assume that the only people on them are folks who, for whatever reason, don't want to fly between Chicago and the west coast or New York and Florida. Trains also serve many intermediate cities, many of which do not have decent air service, or with only very expensive commuter air service. As another poster on this thread mentioned, it might well be almost as fast and certainly a lot cheaper, to get a train from Pueblo to Topeka than flying, if a train was available.