there will always be guys who want a simple day sailor
several boats I have owned never had motors
I sailed miami to key west no motor with the wife and kids
and back in 2 weeks on a old 24ft full keel lead mine
my raven a lite 24ft c/b was 1/4 the weight and had twice the speed
the 18 ft hobie was lighter and way faster then ether and more fun
but if you have tryed to go places a 4-5 knot slow boat takes too much time
I am thinking of the avg guy with a job who can't take off years or even months but has a 2-3 week time and a few long weekends
foiling will extend range by 3x or 4x and turn 4-5 knots to 20
time is the short supply thing that will drive foiling
Extended cruising range is a good thing for some people as you say, but as noted earlier it's not an issue for many of us so therefore foiling isn't in our cruising future, and therefore it is not "the future" - it's just one of many futures. Personally i find my weeked cruising range has no relationship to peak boatspeed; it's related to how enjoyable the return trip will be if the conditions are bad (ie if we have to motor in a dead calm or beat back in 20 knots) and foiling isn't practical in those conditions. And even if we could use our extended cruising range for "2 to three weeks and a few long weekends" would it be worth it if we had a boat that wasn't practical for the rest of the time?
Whether foiling will extend cruising range significantly is another thing, isn't it? Foiling doesn't turn a 4-5 knot boat into a 20 knot boat. It turns something that is already the fastest boat of its type into something even faster. Moths were already the fastest (for their size) and one of the most influential dinghies years ago, and they were made completely of carbon, weighed just 26kg and could beat 505s and Flying Dutchmen even before they started foiling. The A Class was full carbon with a 30' wing mast and the world's fastest singlehander even before it started foiling. The Gunboat G4 wasn't a 4-5 knot boat or most people's idea of a cruiser, it was a carbon ultra-light cat with minimalist interior fittings and an interior that was less usable than some 40 foot racing tris in many ways. It had no standing headroom in the saloon or head, no private double berth, no access from the saloon to the single private berths without going outside, and the galley was in the cockpit - hardly your typical 40' cruiser.
None of those boats is anything like most people's idea of a cruiser (or daysailer in the case of the Moth and A), and once you start making them into what most people call a cruiser surely you'll start to run into problems with getting them to foil properly and regularly, just as you do with the foiling Laser you used as an example.
And don't the examples you give show that speed is all comparative and not very important? By the standards of many people, the "light" Raven is heavy, old and quite slow - there are kids boats (like the 29er and 13' Skiff) that could go faster in a good breeze. By the standards of many people, the Hobie 18 is heavy, old and slow. They are both cool boats and if you enjoy them it's great, but the fact that you and lots of other people can enjoy boats that are (by some standards) heavy and slow shows that pure performance isn't that important. If pure unadulterated speed was what counted, you wouldn't have had fun with the Raven or the 18, but you did. Some of us sail things that can do over 30 knots easily, but we don't find that any more fun than going 5 knots on something else.
While sailing is concentrating on foilers as "the future" and the sport is shrinking, other sports and pastimes are concentrating on simpler, cheaper and slower pleasures and they are growing. We seem to have almost completely lost sight of the simple side of sailing.