We could make it so every abandoned railroad automatically becomes AMTRAK property. Every failed railroad becomes AMTRAK property as well. As AMTRAK reinvests in these and builds a profitable income base eventually AMTRAK becomes the national operator.
We do what I will call the America Plan, where failed railroads become part of AMTRAK and mergers are not allowed. This is what we did in 1971 with the formation of CONRAIL.
The cheapest option by far is full permanent nationalization with AMTRAK taking over every private railroad in the company. Private freight operators still exist, but now they can run on any track which is now publicly owned.
Nationalization is the only way I can see the US expand passenger railroads at a similar rate like what has been seen in Mitteldeutschland.