In all fairness, YS innovation has been a little hamstrung by the 5kg weight limit and the inherent vibration and cyclical nature of the output torque of their engines.

There's been about 100g-150g margin gained by the addition of modern technology and materials, much of which was soaked up with the addition of a CDI. However propeller weight, airframe construction, engine mounting and servo selection are all a little on the beefy side as necessitated by the powerplant. Also, all the (necessary?) dangly bits they like to attach to planes today are subtracting from YS's wiggle room with powerplant weight.

Unless there was some innovation in those areas to give YS 300+ grams to play with, there wasn't really much more they could do in F3A other than continue upping the displacement of a direct drive, single cylinder four-stroke.
Just my 2c.