In this thread it is mentioned that there's not a big demand for a way to program cockpit displays within the SDK.
Is there, today, any timeline when this feature might be released?
I'm a software developer, so I understand that this kind of exposure to external (rendering) code is currently probably not covered by the engine architecture at all. It would really be required for developing more complex (or modern) 3rd party aircraft, though. It might even open up ways to extend existing (default) aircraft. I believe zibo's 737-800 for X-Plane works like that, and I'd really love to have a try at extending the default Q-400 a bit to feature more accurate procedures and maybe a (very simple) FMC.