I am definitely sensitive to wanting to use WASD for other functions. Those are among the most accessible keys on the keyboard, after all.
But the reason why I think WASD would be good for camera movement is that mouse ops are expensive. They take a lot of time during which you cannot be doing anything else. Moving the mouse to the edge of the screen is a very slow and ineffective method of panning.
Directional arrow keys are also not a good option. It's fine if the arrow keys are assigned to do this job, but for serious players those four keys might as well not exist. Actually removing your hand from the main keyboard to go to the arrow keys and then to go back, is significantly worse than mouse movement. Picking up the mouse hand to go to the arrow keys is, similarly, very slow and wasteful.
Strategic zoom is the other viable option, allowing a very distant zoom out, followed by a cursor movement, and a rapid zoom in to a different position. Strategic zoom is why SupCom does not need camera movement keys at all.
The current right click drag pan is workable. But right click is also used to issue orders. So using it for camera movement raises two possible errors; accidental orders when the player intended to pan the camera, and "missed" orders when the player intended to issue orders and accidentally panned the camera a tiny distance instead.
Additionally, right click drag has historically been the go-to button assignment for complex orders, such as line-drag in Spring or formation draw in SupCom and other games. Because RMB is traditionally used to issue orders, it makes intuitive sense that holding RMB is used for more complex, abstract orders, and also makes those orders speedy and opens up the possibility of using the keyboard at the same time.