Three years ago I suggested a smaller version of exactly the same idea. Crossover track from the CTS loop to the tail of the wye and dual gauge to the Antonito station. Trains could be made up, backed to the Antonito Station, load passengers coming on the Rio Grfande Scenic from Alamosa, pull over to the CTS Station, load the remaining passengers and head for Chama.
If passengers coming from Alamosa were loaded first, that might encourage more use of that line.
When I first made this proposal, I was informed that possibly it could not be done because of FRA regulations. My opinion is that since rolling stack would not actually switch between railroads, FRA regulations might not be a problem.
It seems to me that there are a number of major problems in trying to accomplish something like this; who would spearhead a project of this type, does the City of Antonito REALLY want the station are revitallized (they own the station I believe), and biggest of all, where would the money come from.
Another interesting thing in that picture, which is in the book "Ticket to Toltec", is what is the slight bending to the left of the dual gauge in the distance before it comes back to join the main line. I posed this question to Ed Ellis of the SLRG a couple of years ago and he told me that he honestly did not know the answer.