I'm also curious how they would deal with rock deformation as it reaches the point of becoming less solid and more squishy. There would need to be a mechanism to maintain hole integrity post-drilling.

To your question, I'm wondering if they simply pump down water and extract resulting steam once it reaches the point of vaporization? The steam condensers and everything else are already built on-site for coal generation.

One difficulty would be handling any accumulated minerals that got into the steam loop from interaction with the rock in the hole. Unlike traditional closed-loop steam generator, an open system would pick up contaminants and eventually cause scaling.