If I were to design an Ultimate bipe that would sell I'd make it;

Around 65" or 64" span (perfect for 50cc ,but option to install lighter 40cc or 60cc for macho's), not bigger, Godfrey has a perfect 70" Ultimate for the ZDZ 80 or 3W 75.
Quality kit and ARF for those who like either one,
Laser or CNC cut balsa and (lite) Ply (make it light and strong)
Choice of CNC cut foam or built up wood wing,
Quality fiberglass cowl, wheelpants, landing gear and canopy (Stans fiberglass?),
The option quality hardware (Style R/C City) included or not,
Try to make it as scale as possible but have a proven testflyer to help you to design a perfect flying bipe.
Have a peak at the Godfrey Ultimate and Bigairplanes Pitts 12 !
Don't start selling unless you are ready to ship !

Remember, there are no shortcuts , to be on top you have to be the best!

All the luck ,
Bruno.