This is a common concept in software development, and I was wondering if it could be extended to the cockpit instrumentation: It would involve developing a library of current good instruments (eg, ADF's, ASI, VSI, HSI, Altimeter, etc and other meters commonly found in light aircraft)
Then, define an instrumentation panel and an interfacing .xml file that places the respective instrument in the panel (with it's representative model) and connects its inputs and outputs to the relevant systems.
At the moment I guess there's a fair bit of hacking around with the instruments that have been developed for the likes of the Cessnas and Pipers, and why not make this freely available to anyone that wants to use it - a little bit of documentation (perhaps a standard for something like the ADF, Vertical Speed, Altitude meters to make it really easy) and it's part of the root FG data repository and not re-distributed with every aircraft that uses the exact same instrument in the cockpit, for displaying airspeed.
The development process for a cockpit then becomes very simple - decide on the instrument you want in the cockpit, lookup the documentation, include /common/instruments/ADF/ki227 and connect it to an electrical supply and anything else it wants, and specify where the model is displayed on the panel.
Modifying the aircraft (eg, experimental aircraft and I want to try it with a KI228 with an automated sync) can be very easy, just switch the included ki227 for a ki228 and add a second connection
Aircraft developers can then worry about the airframe models, FDM designers can worry about the FDM, the cockpit display systems can be cobbled together very quickly and easily, and with the right methods, can be made to look very much like the real cockpits of some of the light aircraft.
It may not work for glass panels (heck, why not? They plug in a hole in the cockpit of the real thing and just have more inputs to them) but simple instruments ought to work well with this sort of system