All InterpolatedCamera in 3D does is lerp the camera's transform. You can do this in 2D yourself with something along these lines:
export (NodePath) var target_path
export var speed = 10
target = get_node(target_path)
position = lerp(position, target.position, speed * delta)
You can play around with how you move the camera depending on what effect you want. It's really just about moving the camera independent of, but linked to, the target.