It’s never been shared, FWIW. The rails are mostly privately owned and were built that way too.
That said - bullet trains are great but I fully support the ability of individuals to pay to access freight or passenger rail to subsidize the infra.
It was kind of a mixed bag.
Part of the way this worked was that USPS was actually paying for a lot of the rail services to deliver mail (which is also what the government wanted more so than passenger rail service.) The moment USPS pulled contracts in favor of long-distance airmail the whole model went belly-up.
Unlikely. Because they tend to be close-coupled units with distributed power and traction control. In case of anything Talgo-related with https://en.wikipedia.org/wiki/Jacobs_bogie 's even more so.
Land was granted to the railroads with the agreement that they would run passenger rail services. When passenger rail became so unprofitable that it was bankrupting rail companies, they lobbied to make it the governments responsibility to move people around and leave them to make money shuffling freight.