Absolutely Open 100sqft upwind sailing craft

In the US, the open landyacht classes are exactly of this type. Class V is 49 sq ft, Class IV 59 sq ft, Class III 80 sq ft, and Class II 120 sq ft. Sail area is defined as the planform area of anything that's adjustable to the wind. This is includes the sail (if any), mast (if any), boom (if any). There's also a requirement that major structural members can't be changed during a regatta - this avoids having a whole series of rigid wings for different conditions. Other than that, pretty much anything goes. Today's trend is toward high aspect ratio, producing some surprisingly large yachts for the sail area because the platform size has to grow, too.

Instead of a sail area limit, another interesting approach might be a height limit. This goes directly to the issue of righting moment and induced drag. For a high-performance craft, more sail area is not necessarily faster - it's L/D that counts. But it allows you to pile on the sail area for downwind legs, making for spectacular sailing. With a height limit, there's no need to restrict the beam, because there's no point in making it wider once you've balanced the limited height of the center of effort.