I think that anyone seeking to restore the San Juan extension would probably first need to hire legal counsel to find out what the ramifications of the abandonments were in Colorado and New Mexico. Did the land revert back to the original owners? Most certainly, there is a legal battle ahead.
Prior to the details of equipment, etc, we need to find out what the situation is with the ROW. Obtaining the ROW would be the first priority in my mind.
One comment: Maintaining a length of track in the middle of the abandoned ROW makes sense to me. If a legal battle should occur, one might be able to use "eminent domain" arguments if they were connecting existing rail lines.
It's a long shot, I know, but it's fun to dream about possibilities.
Jim Burrill