.has Standard Class Design reached a plateau?
and if so where do we go from here?

While othewrs had argue the merits of various building methods these do not
directly offer any performance improvments. Given the size of most of the
production runs I would look at vacuum infusion for wetting out the cloth.

Aerodynamically the place to go is reflexed airfoils. Note: I did not say
flying wings. Reflexed airfoils can operate quite well on tailed gliders and
this configuration offers many pratical benifits.

Robert Mudd