Possibly, the largest constraint in the development of kit, or homebuilt helicopters, is lack of a source of blades.
As a start to bugdevheli's "Lets make a helicopter", what about a team effort toward the development and production of blades, only? The equipment could be given the capability to produce a variety of blade sizes. For example, the largest allowable blade might be for a 2-blade helicopter at the maximum weight of the new Very-Light categories. This equipment would also be given the capability to produce smaller blades for lighter helicopters, and/or for helicopters with more blades.
Alternativly;
IMHO, the single greatest improvement in rotorcraft will be the development of
Active Blade Twist. Specifically, an ABT that is capable of large twist at a high twist rate. There is no reason why a group of motivated people on the Internet cannot compete with the universities and companies that are currently looking into ABT.
There would certainly be a market for very-light helicopters, which due to an improved L/D ratio, had a quantum leap on existing helicopters.
Dave