Your post reveal good intentions I'll give you that. Sometimes I miss the simplicity and accessibility of windsurfing as it was.... But there are many reasons for the situation as it is now, debated to death on this and other forums. I firmly believe we we will NEVER see the numbers from the '80s again, is the sport going to die because of that? Don't think so.
"Main windsurf companies would agree on one board and rig design, then would allow any windsurf company to manufacture and sell it under its own brand"
Somehow I just can't imagine that happening.
Furthermore, I can't see how can a board be pleasant/accessible in light winds for beginners, but also performing/controllable in force six (depends on what is controllable to you).
Pg is right, I think Kona comes closest to your ideal at the moment.
Please take no offence and good sailing
PS I've said it before: as a photo enthusiast, I would like a lens 10-400mm F2.8, not too massive/heavy, high performance, affordable if possible. Not gonna happen (anytime soon)