Hello,
Can anyone tell me if it would be technically possible to replace the camera of the Air Unit O4 with that of the Avata 2 with its tilt system?
If DJI goes through this, it would be an interesting development I think to have a tiltable camera for the next Air Units ;)

You cannot. But there are some third part gimbal out there. Actually just with DJI O3 or Walksnail compatibility.