If speed is key, what about developing nuclear-powered TBMs?
Also, see e.g. https://en.wikipedia.org/wiki/The_Core for prior art /s
If you put a nuclear reactor underground, you have to pump water back up. This takes a lot of energy. Whereas, electrical energy travelling through cables is not affected by gravity.
https://www.youtube.com/watch?v=9-_xfTUs3R0
(These things are pretty inefficient, but it'd be a way to wrap SpaceX into this new company along with Tesla.)