In order for the line to be profitable, I believe that you must have freight. And that means Diesels in order to be competative with trucks. Maximize productivity and minimize labor. Also any service from the airport would need to be modern and relatively fast. As far as freight goes, Coal would seem to be a possibility if there is a need in the near future for a power plant in SW Colorado. The economics of having to reload in Antonito and keeping the C&TS open year round would have to be factored in.
I say this due to a recent occurence in Missouri. The old Rock Island line from K.C. To St. Louis has not had a train travel down it since 1979. When the U.P. decided to abandon it a couple of years ago, a company made a bid to buy it. After long negoiations they finally bought it. Only after the sale, the new owners announced that they were owned by EMRON (not sure of the spelling), but used to be Union Electric of St. Louis. They bought it just in case they needed to build an additional power plant in mid Missouri.