Your comments

I think none of the above solutions are feasible.

By overriding coerce value callbacks the limitation would be applied on the camera not for rotation only. In real life scenarios, I might prevent my users from doing such things but I don't want to limit myself. The correct way of doing this would be to open the mouse handlers to be extended, or create a callback or handler that could modify the rotation delta before application.

I don't really understand why these handlers are completely hidden from the developers.