Does sharing track ever work? Amtrak already has to share track with freight, and that's why Seattle to Portland is officially "3.5 hours" but the margin of error on that is +hours.
Even so, I'm guessing that there are options other than $50B of high speed track to improve the route. Maybe there's a few segments of track where a large fraction of the delays happen, and 30 miles of amtrak-owned track would really improve on-timliness. Just getting it from +hours to +minutes might draw some new users.