I see RC helicopters seem to be set up this way as well, obviously different scale of loads but surely it proves the concept?
I don't think the practical advantages of ease of storage , safety and ruggedness of a small rigid 2 blade trainer are lost on the manufacturers. Especially the "boutique" ultralight helicopters that seem to crop up every year or two in Italy or Eastern Europe. But they are competing with the likes, handling and ride of a Cabri or S300. If it rides like a jitterbug/buckboard and needs a functioning SCAS to make them manageable as the RC ones do, maybe it's just easier to deal with the third blade.
Interesting that we don't see helicopters beyond the light/intermediate twin class marketed as "rigid". They all revert to fully articulated. Might the same phenomenon of scale be at work as we progress from rigid head rc toys to full size underslung teetering machines?