But even then, not every display-enabled SoC is well modeled as a dumb framebuffer. The Raspberry Pi itself provides hardware overlays, and it's quite problematic to expose them under that kind of model. The DRM infrastructure seems to be a lot more general and flexible.

I wouldn't recommend an RPi for product development. There are better SoCs, like i.MX, with documented graphics pipelines and graphic/video/camera overlays that are easy to use.

Incidentally, i.MX6 is an example of using the Linux fbdev with hardware acceleration.