As far as I know OpenGL does not support rendering from threads. Maybe something changes with time but if not...
Also I don't think that proc-oriented style is useful. I'd like object-oriented one.

As a main (and only) quad-engine developer... hm what can I say. Code abstraction must be as greatest as it can be. Thus can help in fast development later. But I think that if developer really wants to use all low-level stuff (direct opengl management, or winapi etc)