I seriously question "massively profitable", especially if you do it as a private company. You'd have to buy the right-of-way, and then pay taxes on it every year. That's some pretty expensive real estate. Then, the maintenance requirements on high-speed rail are pretty stringent. That costs, too. It's not just the cost of the train crews and the electricity (or fuel) that you have to think about.

If you've got real numbers, I'd like to see them.