Financing isn’t the issue. If we can finance an endless war, we can surely provide funding for a rail system. However, interstate transportation falls under federal responsibility. A private company cannot retain financing from another country and just go out a put down railway tracks across the United States without federal involvement or even across a state without the support of the state.
Even in the case of Florida, where federal money was being given to help create a high-speed train, the state refused the funds because the state legislators did not want to provide the matching funds necessary. The state could have provided the money but chose not to — a political decision — and a very anti-Obama decision. Our Republican legislature would never agree to fund an Obama-supported project, no matter how good or needed the project might be.
Of course, if the federal government was behind the idea of building a modern rail system, it has legal means to so so without the cooperation of the states, but private companies would be hard-pressed to win eminent domain cases in multiple states. Litigation would tie up the projects until all those involved were dead!