So we agree that specific races are driving the interest in a formula 20 class.

I suspect that the Tybee would allow an open class if you had 5 boats interested. Moreover, I believe the racing would be fairer on a measurement handicap rule then fitting your existing boats into a formula box and asserting that the racing will be fair under the formula.

Remember, The proof of a formula rule is on the water and knowing that it's fair is a precondition to getting good participation for an expensive to compete distance race.
The F18 rule is proving to be fair, Even the very pro development A Class formula rule is proving to be pretty fair... a (Flyer I pulled a top 10 finish in a Race at the worlds. The F16 rule on the other hand generates controversy and boats that have different ratings.... time will tell if the controversy that we see now is just noise or the rules need tweaking. I don't think you can underestimate the need for boats allowed under the rule to actually BE level.... not just mathematically equivalent.... otherwise... your race turns into a tour.