My request for terrain engine would probably go hand-in-hand with the graphics engine. I would like to see an improved rendering of objects on the ground (in the air as well) at long distances. For example in War Thunder, you can see roads and trees for many miles away but in Aces High, you have to keep your detail range turned down; else the game consumes massive amounts of resources and overall performance decreases.
Other thoughts on destructible objects in terrains:
1. When a client is connecting to one of the arenas, during the loading screen, include a fast-check of destroyed objects reported by the server. When the client is finally connected and in the arena, all of the data has been loaded and only needs to be rendered when the client is within visual range of the object.
AND/OR
2. Each client will only request updates from the server of destroyed objects that are within 4K range (or at any given range) of the location that the client is on the map.
Also another beef I have is that the sun sometimes shine through mountains. Also if you are flying behind a mountain with the sun on the other side, your plane/cockpit should be darker as there is less light.