To jakozaur’s point, there’s plenty of reasons drilling can get cheaper and there’s at least one other company working on it [1]—would love to hear about others! I’m a minimally informed amateur but my intuition is that the way it’s typically done (multiple inch borehole, U-tube geometry) is fairly suboptimal since the diameter is a lot wider than you need it to be just for hydrodynamic resistance and you get losses from the outgoing liquid cooling the incoming liquid. Dropping the diameter should make drilling a lot easier—-you can sink a 5/8”x12’ ground rod with hand tools in the right soil! (you’d still have to figure out how to make the holes meet up but I imagine there are ways of doing this).
The fact that you need to roll out a drilling rig plus crew at all is going to be a large part of that cost. For it to become interesting for the average homeowner the price is probably going to have to drop by something like 75% - but that basically kills any margins for clever new innovations...
What I was trying to get at with the ground rod example is it’s entirely possible that you wouldn’t have to roll out a drilling rig and crew. To zoom about a bit, the main risk for heat pumps is really ugly winter peaks but besides that, ASHPs are perfect 90+% of the time. So the main role I see for GSHPs is backing up ASHPs to shave that peak, and once you scale back their role like that it seems like there’s a lot of ways to cut installation costs significantly.
In some potential future, there is an engineered a plant/fungus in a pot that you place onto the worksite. Months later, with regular sugar-water and hormones, it gives you a root-pipe for pennies a day.
Of course at that point we might not need the cheap pipe in the first place.
Nanobots that manage a plant / fungus / bacteria/‘ / amoeba workforce.
They drill and line boreholes to both anchor the foundations of the building and provide a closed loop system for a reticulated-water ground-sourced heat pump system.
They also use the soil recovered from the boreholes to build the soil-polymer foundation.
In the future, pallets of nutrient-cement are placed on the site and the bio-borg-bot farm also builds the entire building, including all the plumbing and wiring and windows etc etc, with the added benefit that it all looks like some weird alien / xenomorph Gigeresk hive excretion.
That reminds me of a less grey-goo-adjacent idea from a Larry Niven book, in which the base-structure of houses were cheaply made by growing a kind of coral inside a watertight scaffolding.
Given the last few centuries of humans under-estimating nature, I predict that many "nanobots" predictions will turn out to be a kind of optimistic hubris. We'll end up making comparatively minor tweaks to the massive base of existing nanobots called biological life. Especially the multicellular varieties, which have many tested and integrated strategies for building things, such as the towering bipedal mega-fortress my hive mind currently inhabits.
[1] https://www.borobotics.ch/