There should be categories and 3rd party developers need to make sure their plane fits into at least one. Eg. DCS Fidelity, Flaming Cliffs Fidelity (you pay for the aircraft to be added to FC3, you don't pay for a standalone FC fidelity aircraft) and DCS Fidelity Civilian Aircraft (that is if people want civilian aircraft). I think ED really need to keep a close eye on what they let in as I think they could ruin what DCS has going for it by introducing a whole load of inaccurately modelled super planes that will auto lock you from 20 miles and have a 2.0 thrust/weight ratio.
What I'm trying to say is: I don't want DCS: World to become the new FSX. I'd like it to be a real world combat simulator where you know that whatever plane you buy is of the highest fidelity and that you won't be dogfighting super planes in multiplayer.
I would also like to see terrain addons for new parts of the world, however, I wouldn't like to see terrain improvements for current terrain (unless as a free update as part of a patch) as I think that would soon turn into a bottomless money pit.