Vacuum maglev pipes require cooperation from the people whose land you’re going to take via eminent domain.
Do you think that kills the idea? We have two major cities with 300km of mostly farmland in between where I live, so I'm pretty sure it would be no problem here - if investors would fund it.
Higher speed trains need much larger turn radius so existing RoW is not suitable. They’re running into the same issue trying to build high speed rail into the SF Bay Area.