Although I understand your point, LED and GPIO differ quite a bit.
First of all, GPIO bitbanging requires often some precise timing, something that is irrelevant to LED and other "human display-only" interfaces.
Second, GPIO are usually "tristate", meaning that you can program the pin to be left with high-impedance. LED class not only does not implement that, it does not have to implement that at all.
IMHO, GPIO-style pins, on specialized hardware, should have an interface very much like USB has right now. Meaning, to be able to be bound to kernel devices, and to be claimed by userspace, with somehow same rules like those on current USB stack.