There is a mod that Indrid used, I believe Myrdal used it, so if you could ask either of them they might be able to help.
A zoom mod would not be compatible with multiplayer because of having to use -dev to make it work, making your game effectively a different version to the one people are playing. I also doubt it would massively affect balance if it did somehow work with other players because all maps in the game have distance fog that varies from map to map, meaning on some of them you would only need to zoom out a little before not being able to see anything, and on the ones you could see, objects will start to despawn and you can't get any advantage if you can't see what you're fighting.
Wise Windu wrote:From what I remember, maps have built into them a sort of net over the top that constrains the movement and zoom for the camera. For a mod of these, someone might have to go into each map and change that.
Not quite, its more like a net that the camera sits on top of, so if you raised it it would just make the camera float higher above the map by default, not letting you zoom in and keeping you awkwardly zoomed out all the time.