Yes, I know this should be in the Features section, but it won’t let me post there, so oh well. Here goes.
I know some of these have been recommended before, but might as well freshen this up. I propose that additional airport details (taxiway signs, various buildings, and GSE) are added as options to the game. One argument is space, so implement them in a system similar to how you download the various aircraft. When you go into the region menu, you can click either on one airport or have an option to select them all, and there would be various check boxes to download different things, such as one box downloads GSE (Ground Service Equipment).
Next thing I have is AI traffic. This could be for both solo and Live, although it could cause some issues for the already overworked ATC. This would help give more of an immersive feeling to the game, especially solo. There could be three settings; low, medium, and high. These would allow you to chafe the amount of AI traffic, or turn it off completely.
Finally, automated ATC. I propose that this would be only for solo. I'll use the example of my beloved FSX. You get an ATC menu, where you select different things, each one asks the ATC something different. I haven't played Live, but I assume it's something like this. Basically, it's the control system from Live, but just a robot controlling it.