On a related note, even Amtrak with owning their NEC (Northeast Corridor) that runs between Washington DC and Boston and has a massive population along the route...fights to stay solvent on even just this route.
And of course they need large subsidies for other routes, even when using other railroads trackage.
So while I would love to see a Miami to Orlando train route succeed...for the life of me I can't see how it could.