Honestly even just double tracking all of the mainlines where they aren't already double tracked would be game changing for throughput. Having the federal government handle maintence and dispatching would absolutely re-align values and greatly improve the passenger experience as it is though.

For context, Amtrak in the 90s and early 00s ran express freights and the big freight railroads hated competing with Amtrak because Amtrak generally did a pretty good job with it's freight services. So basically forcing the freight railroads to compete on more than just who owns what right of way would greatly improve both passenger and freight transport.

Personally I'd love to see a dollar for dollar requirement for all road improvements to spend an equal amount on public transit and pedestrian/cycleway improvements. "Oh you're spending 10 billion on this new highway interchange? Here's some bike path improvements and bus system improvements you could sink another 10 billion into to match"