There was a great thread a while back on the Honda EXP-2. The clean burning 2-stroke, that used a rotary type exhaust valve, to clean up emissions. The new CR250 engine is based on that design. I will do a search to try to find the thread. As for the dual plug theory, my old Nissan pickup truck had it and it seems to make sense, especially for a 2-stroke, but what I gather is that manufacturers design simplicity and having another spark plug might complicate things for home mechanic's (Jetting, expense, electrical, etc.) While in a 4-stoke application(especially in cars) maintence isn't an issue(there hardley isn't any) so a dual plug design would work.
Erik