Well, it's a good topic, even if it's been discussed before.
With the way technology keeps re-inventing itself almost on a daily basis, it's nearly impossible to put something out that'll be compatable with everybody's equipment.
But I think that a game should have the best of the sim legends in it's core before they go and try and re-invent the wheel.
Just a small example:
Jane's WW2 Fighters - the hotseat and an ingame respawn option, waypoint event switches (mission builder), split braking!
CFS2/CFS3 - interactive cockpit, unbiased flight models, damage modelling, split braking!
IL2 - game engine, video rendering, broad range of user defined aircraft controls, video recording (track).
Then build on it from there...