I can't address the needs & nuances of drilling with a plasma torch, but I've done a lot of work in thermal coatings applications with plasma.
The heat generated is derived from an ionization (actually knocking an atom or 2, depending on gas used, off a molecule) of an inert gas, like Argon or Nitrogen, via a DC current passed between 2 electrodes with the gas present in a controlled 7 directed vortex or channeled manner.
As a result, the actual internal heat enthalpy inside the torch (gun) is around 20K F, & just external of the torch (doing the work) is around 4500-5000 F.
It would take a pretty big DC source & really long cables with a lot of loss over that kind of distance...........just practical problems that have to be solved.
Interesting concept though.
MM
