Hi Flexman,
As requested, here's what I think would be a good starting point based on what is available currently in EECH.
Any indicator lamps in the cockpit (on/off).
MFD displays either exported or made available for third party software to export (MaxiVista).
Aircraft heading, speed, altitude, pitch, roll (last 2 for the guys who what motion platforms).
Be able to switch ALL on screen cockpit graphics off. (so you can project external view)
Possible addition would be to export the hud data (to allow display on a small monitor on the helmet.
Not much to ask he said extracting his tongue from his cheek !!!!
Format for the extracted data would be to suit the SIOC program, which is a freebie from Opencockpits website.
Cheers,
Andy