It depends on the type of system you're speaking of. For the individual homeowner, I think it would only be practicable at certain points. Again, as Thomas has mentioned, let's say your furnace dies on you. You, at that point, have the option to purchase a geothermal system. It's going to cost you more initially, but where you're going to save on it is in your operating costs of your home. You're essentially not going to have energy costs other than electricity to run the geothermal system. So, yes, there are opportunities out there that could be employed.
Now, incentives to help retrofits make use of that type of system would be good to incite the homeowner to take that option on.
The other option I've seen is utilities providing that particular system and overriding the cost of it, so that the homeowner doesn't bear the cost. The homeowner continues to pay a monthly bill, just like they did for natural gas, except that the utility would get the monthly bill and cover the capital cost. So those types of things are being explored.