I like the idea, though having a direct line of sight to bedrock similar to MFR's drill could also work. The higher you build it, the more ridiculously expensive it becomes to drill down, and maybe implement a small heat loss over distance?
It would make Greg's life harder. (coding a block pipe, that stops the multiblock operation when broke...)
I rather have it close to bedrock, looks cooler. There is no "close to bedrock" dependant generators (aka real geothermals) at the moment.