Presumably the rod at the top of the rig has to support the weight of the miles of rod that's attached below it? Is there an engineering solution to the problem of supporting an increasingly heavy drill rod?
One could fill the hole to help float some of that weight, but that would only cover about 1/8th of it.
EDIT:
Turns out, things get hot pretty quickly with depth;
Only need to go about 3 miles deep to start hitting boiling temperatures.
Seems like we need more boring.