The FRA's regs are rediculously overprotective. In this day and age though, you will not be able to relax them. What the pax railroads can do though, is slowly erode away the de facto status of the FRA regs. In NJ, the former Nelly-Bly (now the RiverLINE) is under a timeshare agreement where non-FRA complaint DMUs can operate on the line in a tram-train configuration, with street running on non-FRA rail in Camden as long as they are not running on the mainline tracks between 10 PM and 6 AM. The cutoff to freight is later on weekends. Once something like this gets established on a high-speed line, if the time for freight was gradually reduced to perhaps a 12:00-4:00 slot, you could have a line that for the most part, wasn't subject to FRA regs. You could then run modified TGVs or ICEs configured for 60hz power in the US, without having to build a new line or isolate an older one from the national rail network.
"The Erie only sells 1 way tickets on the NJ&NY because it only has a 99 year lease on the line."