Design envelope for a F20ht class? I am in for a homebuilt 20 footer, but not down to the weight of a M20 or similar.

We have discussed this before on this group, ad nauseam. There is interest, but not many willing to commit before there is some activity. If you want a class to grow, consider cost and ease of use (e.g. legal trailering width, glued beams etc.).

To grow a new class from infancy I think you need a very strong manufacturers support or a homebuilding option. A combination is best, like what the F-16s did.