Both good questions. To the latter (price) question I'm sure it's only a matter of time/interest before technologies for design/production reduce the overall cost to something akin to "reasonable" for a high-performance boat.

The "Fad" thing is more nebulous. As you indicate, it is expensive and requires a whole new skill set. Right now we're seeing the 'early-adopters' developing the platforms through trial and error. I suspect it will eventually disseminate to high-performance racing oriented people and therefore show a bit of success albeit at the expense of further dividing up the small racing community into another fleet.

But, to be a game-changer in terms of its long term success, I suspect it will have to be a technology that can appeal to a wider set of sailors: namely those part-time racers (cost) and recreational sailors (cost vs. ease of use vs. durability)

The H16 is a perennial favorite because you can race (OD or PHRF) if you want, or strap a cooler on there and go gunkhole for a weekend with family or strippers. The price is reasonable for both racer and non-racer, the boat is reasonably durable, etc.

Will the same be true for a foiling cat? I don't see many moths out for a cruise with kids (they probably should), and I can't imagine the challenge for foiling on the Steeplechase (sandbars) or Miami Key Largo route (seagrass). Would you be willing to take non-sailors out on your $40,000 boat "just to tool around"?