When Francis Reynolds, the one who named the idea, spoke with me years ago, he said that, like you, many of us have had the same idea for a long time. It is actually an obvious thing, once we stop to think about it.
Also, HiLoMag is the next step in the evolution of interstate travel. Since Eisenhower already gave the nation the right-of-way, that is not a cost factor. And since the elevated rails would never wear out, the initial cost of building over the existing interstate system would be a one-time expense. This is win/win.
The cost of 3.5" diskettes was extremely prohibited when they first came out. 5.25" was so much cheaper. But by beginning to purchase and use them, the 5.25" disks went the way of the dinasours very quickly. And so it goes. It was a simply desire for convenience over cost.
Convenience often wins out because of the demand people have in this fast-paced life. I have stopped calculating the cost of the obvious. IMHO, it is counter-productive.
HiLoMag would be an excellent national project. Especially at a time when we desparately need to put many to work.
Old rail beds might be used, but as you implied, they are in the private sector. But some might be deeded over as they are closed down.
But to answer your question. The same national/state ownership of the Interstate Highway System would own the elevated maglev rails. They would need to expand their infastructure to include the computer control systems only, but the nation would gain the needed expansion to the electric grid as well. Another win/win.
Once you study the concept you will see that you and I will still own and operate our electric vehicles. They would operate around town as any of them do now. We already have the necessary range for daily use. We already have the proven technology for daily use.
All that would be needed would be a change in the design of new vehicles to fit the rail system with one-half of the induced-current linear motor system to mate up with the matching part on the rail. Plenty of work for the existing auto industry for some time to come. In fact, they might have to expand production for a while.
Freight would simply be done in small quantities at a time. I can imagine no problem with that whatsoever.
No more road repairs; another win. No more acidents or need for police or emergency vehicles; another win. Obviously, the costs would be driven down so hard that even if the cost of electricity doubled, it would still be a huge gain in transportation cost reduction overrall.
There would be no more pollution from highway transportation. And since the times are as quick or quicker than intranational air travel, there would be no more flights over our nation, thereby reducing pollution even more.
What a fantastically great idea whose time has come!