The big issue is getting an agency willing to acquire it and funds for it. UP can easily be persuaded to let it go, easy money for two streaks of rust that have gone unused for decades. That first step is a doozy, everything else is trivial by comparison (btw, the signal infrastructure will have to be entirely rebuilt. It was old and code line based, and is effectively gone). Getting the political buy in to do it is the actual hard part, especially in Arizona. There are no on line communities and no service to the non existent communities to build support on.
Doing Tucson-Phoenix corridor service on existing, serviceable track is the logical place to start to build ridership and awareness in southern Arizona. At least it goes through existing communities such as Mesa and Tempe. Maybe after such service is established and popular, a case for Corridor service to Yuma, the Coachella Valley and Los Angeles can be built. That is case, once built for Corridor service the Sunset can use it. Building a case based on the Sunset is the tail wagging the dog.
Starting with Phoenix West is simply a recipe for political failure.