The problem is in the cost of development. Certainly there is always room for the development of new engine designs. Take a look at the twin piston/cylinder two stroke designs the Germans are currently working on. However, the cost is prohibitive. You could adapt a snow mobile engine such as was done early with a UAV platform but there would be a lot of additional time, labor, and expense in doing so. Rotax already has several powerplants availble that meet or exceed the needs of just about any ultralight that fits the legal description. Going from ultralight to light sport aircraft and you already have another group of engines that fill the need.

Any of those engines would come up untold thousands of dollars less expensive to use, and have already been thoroughly flight tested to assure long term reliability. So unless you're brutally wealthy, or have an engineering staff and production facility that needs something to do, developing a new two stroke is just not a cost effective project.

Now if you could come up with something light that would run as a two stroke on diesel fuels and not generate a cloud of pollution as two strokes are prone to do you might have something. Design a "green" two stroke that develops greatest torque at under 2500 RPM without gearing and does not suffer a power loss in doing so? That would be a lofty goal.