I don't think it's up to Amtrak at this point. All Amtrak can do is ask what the host railroads want in return for a one-time schedule change and then beg congress for more money to pay them off. I don't see our current congress spending any more money on Amtrak. Nor do I see the host railroads substantially discounting their fees. All of which probably means that no major changes will be coming anytime soon.
Actually Amtrak could do a lot. Here is what I get from the Sunset Limited PIP. The plan emphasized the change to daily service for which the UP has asked for 750 million dollars. However when you get into the plan and read the details, much of what they wanted to do could be done to the existing 3 times a week trains right now and for little or no cost. For instance, schedule changes....leaving LAX much later, around 11:30PM is what the Sunset used to do before the UP melt down and Katrina. This would put Maricopa, Tucson and Houston back to normal arrival and departure times. Westbound they proposed an early morning arrival in LAX much as the train used to do also. The schedule changes, both ways, would eliminate much of the layover for the Eagle through cars and restore the eastbounds connection with the Coast Starlight. Equipment usage improvements could be implemeted by either restoring service to Florida or accepting it's demise and changing the layover times in NOL. Currently Amtrak has at times two sets sitting in NOL waiting to return westbound. This is because the schedule is set for a continuation on to Florida which does not happen. Crews sit in NOL getting paid while they do nothing. It's shameful and a scandal.
Here are some of the goals as listed in the PIP:
Service time improvements
LA arrival marketability
Daytime service in major markets
Restoration of CS connection
Reduction of the SAS layover
Optimization of train and engine crew expenses
Optimization of OBS crew expenses
Better equipment utilization
None of these are dependent on daily service. They could be done now and should have been done long ago.
In addition the plan mentions the possibility of a bus connection to Phoenix which of course could be done right now also.
These PIP's were part of Section 210 of the Passenger Rail Investment and Improvement Act and required Amtrak to identify the lowest performing third of their 15 LD routes and develop an improvement plan. Apparently the act doesn't require Amtrak to implement any of these plans. These plans are out there for the other trains if you wish to read them. None of the improvements have ever been implemented as far as I can see. What this means for the future of LD trains I will leave for you to decide.