Hi!
I think I understand what you have in mind.
For moving the camera with your mouse, there is probably nothing we can do with the WoW API. Because once the player enters the mouselook mode, we cannot register mouse movement any more.
(see
https://warcraft.wiki.gg/wiki/World_...aft_API#Camera)
For keyboard movement, there might be a way.
Hooking the Move{Forward,Backward}{Start,Stop} functions in combination with GetUnitSpeed we could zoom in and out accordingly to make it look like the camera is inert.
But this would only look convincing while you are looking at your character from the back.
Similarly we could hook Turn{Left,Right}{Start,Stop} to pan left and right so the camera looks inert.
But is this really something you would be interested in?