Rivers with bridges. If a bridge is destroyed, vehicles from nearby bases cant spawn near enemy bases at the other side. And some V bases near the bridge edges to defend it with the hability to spawn vehicles and PTs. Even do the bridge transitable by GVs, and we can have some funny GV battles between enemy GVs from bases at the two bridge extremes.
IMO, all this should be easy to implement because the bridge could be done from the CV model, but static. So you have a destroyable, transitable and big object that can be placed heading anywhere depending on the river orientation. The only "rare" characterisctic is that this static "ship" is not owned neither controled by any country.
