I would be afraid of the PCB traces delaminating after many strain cycles. Based on all the cyclic loading and shear flow, I'd imagine they wouldn't last as long, and although the benefits of a softer bottoming out are good, they're effectively negated by "proper" typing methods on mechanical keyswitches.
PCB mounted browns on my huge G80-8113 feel better than the plate mounted ones on my WASDkeyboard, but I like the design of plates more.
Actually, My "ideal" keyboard design is like a DOX plate, where it's bent over, making a stand as well. Simple, elegant, effective.