One thing that sealed the fate of the Tennessee Pass line was the fact that it was rapidly getting worn out. The line could not support 143-ton loaded coal and ore cars. Cars that went over the line were limited to 267,000 pounds.
The line almost went the way of the dodo bird years before as only one westbound train per day plied the rails between Canon City and Dotsero. The crew was deadheaded back. Only after the Rio Grande-SP merger that it got a second lease on life. However, M of W forces were behind on getting the line up to spec.
Granted passenger cars aren't that heavy as loaded coal cars but it points up the fact that if UP was going to make a go of it, it would have needed to put forth huge amounts of green stuff to get it done.
The line isn't getting better after sitting idle for more than 10 years. It would take millions of dollars to get the line ready for passenger service.