These systems are pretty popular, even my dad has one. The problem is they're also pretty expensive -- on the order of $20,000. At that price it could take a long time to hit break even, at least in the U.S.
With improvements in refrigeration technology they may never. If you compare installing geo-thermo 10 years ago vs someone who installed an air source heat pump, and then upgraded (at optimal times picked on hindsight), the latter has paid less for equipment, and his yearly costs are now less as well. Geothermal equipment is enough more expensive that upgrading doesn't help those numbers much even though the expensive pipes in the ground are still perfectly good.
Of course there is eventually a limit in efficiency gains. When you reach that limit geothermal has advantages that will pay off eventually. 10 years ago at least you should not have installed geothermal. What the next 10 years will bring is beyond my knowledge.
According to this [1], the 2015-16 estimated average residential winter heating bills for a propane user ( the highest ) was $2,569. The cost of this system is approximately equivalent to 7.8 years of heating costs. If this system saved 50% on the bill then it breakeven is about 15 years out. These numbers aren't too far from solar historically, if I recall correctly.
The main expense is digging the trenches. If this is done before the house is constructed, i.e. you've already got the backhoe on site to prep the site, the cost should be minimal.
"Expensive" is always relative to the overall cost of construction. For a $400K home being custom made that's not as huge a hit as it would be to some place that's a $100K fixer-upper.
An in-floor heating system can easily cost $5K or more. Installation is the big cost on these things.
Expensive is already relative to the alternative. If a furnace can provide the same comfort at $5k, it takes a long time for the cost savings of the heat pump to make that up.
The real savings is that in new construction, you don't have to pay the extra cost to retrofit.
