I think the differentiating point in this request is that it is for a very specific device (and if Apple suddenly shows off something more fancy, this would repeat again). However it is wise to keep a software generic.
On the other side, gesture capabilities in hardware are nowadays as common as orientation/motion sensors in mobile devices. We are not anymore in the era of only left/right/double click. Where would we be if SketchUp refused to support the mouse wheel? If operating systems provided input interfaces (as simple and standardized as on the web) that are generic enough to cover all such devices, it would make sense to think about it. This would have to be available on all supported operating systems.
As for 3D Connexion, the proper solution would be to have a driver that outputs generic input events instead of writing a myriad of plugins to add support into every possibly software. When I see how well the space navigator works (without 3D Connexion drivers installed) in web browsers with standard web APIs, I believe 3D Connexion's SketchUp plugin would be totally redundant if SketchUp listened to generic 6DoF events.
So actually, if the need pushes enough, a user could write a plugin for SketchUp that uses Apple's magic mouse / trackpad APIs and makes the camera move, just like the SpaceNavigator.