For a new DLC, I also really like an opfor campaign or an ONU campaign/scenarii to change a bit. And, of course, I want a difference which justify to pay the content.
For the engine, like all of us the possibility to fire from passenger seat just miss. The possibilty to decide which faction is ennemy instead of the blue, red and neutral will be a big improvement. And finaly, better ai drivers, it is just ridiculous today.
The editor needs some update to add the 3D editor (it will be so useful to place object to see where they really are) and gui to set the modules instead of a command line.