:: I wonder - what do you think of the stresses a sail rig would put
: on a SOF sailboat like this?

What Bill said. There are lots of examples of SOF sailing boats. With ply frames it's even easier, though. I'd just make some of the frames around the mast and dagger/centerboard case "full" instead of open. That is, they'd be like kayak frames in that'd span the boat at some of the upper chines, too, if that makes any sense. And, I'd add knees to various parts, to resist twisting under sail.

Here's a pic of her on the water, with spokesmodel Anna at the oars. The boat, which we floated on the Shenandoah River, in the Shenandoah county section of the Shenandoah Valley, VA - and which I'm now calling the "Shenandoah Whitehall" (as opposed to the original "New York Whitehall") - rows just great with one or two, and is fast, stable and relaxed to use. I couldn't be more pleased (except for the sheerline, which flattened out when I put her together).