So dumpstatic and I agree - 5.x is a critically important size for the health / rebirth of windsurfing.
As his old thread suggested, there are old boards lurking out there. The local club seems to find them all the time - people keep showing up with some early 80's board (and a few from the early 90's). The year I lived in Montreal there was a guy with an original windsurfer (and sail) who only showed up when it was really howling and the only thing he ever did was old school freestyle. There's a guy here in Ithaca who's not much different, other than being substantially less skilled. Brings his Windsurfer, rigs a blown-out sail, goes out and back, never planes, isn't interested in new gear, drives a Volvo with all his stuff tied on top of the car during the season. Oh, and he doesn't have a harness. He looks at the new gear, might chat for a bit, rigs, sails 45-60 minutes and goes home.
I think to get to these kinds of folks, one would have to have an inexpensive one-batten sail, an inexpensive low-tension 30 carbon mast, a stubby alloy base to fit the mast and some adapters to fit the old mast tracks (more than anything else -THOSE ADAPTERS- would sell like hotcakes). They don't want a new board, but would probably get a new rig if it were $250.
These are not Maui-style modern windsurfers. They're inland lake cruising windsurfers who's other choice would have been a Sunfish (which hasn't changed in about 100 years, save for materials in construction). From what I've seen, both here and in other parts of NY / PA where I've lived, there are lots of these folks. They're the 80's windsurfing boom sailors that gave it up, but who still have the board because....well, have you ever tried to sell an old windsurfing board? They won't spend a lot of money because they've "been there, done that, I'm older now...", but for half-a-dozen times a year they might spend $200 or so.
Don't believe me? Start up a club, give it a little PR, and they'll show up to see if you'll buy their old board...the challenge is to get them back into the game some 25 years later.
One board, one sail, cheap enough to just leave on top of the car, ready to go when you've got an hour or two and the freedom to just rig and get out on the water for some time communing with your God. That WAS the windsurfing boom (I missed it, but the allure of that was why I started). If anything, I believe the yearning for that retreat from the chaos of modern life is stronger than ever. The demand is still there, but mainstream windsurfing has left these folks behind. The answer to that just needs to be simple, cheap, easy to use, and not very technical.
This is a big part of why the RSX was such a screw-up, and dropping the IMCO was a catastrophe.