Basically this strategy works but I am running up against a problem with it (aside from being a bit clunky unless you run a very tight loop). You can't really set the camera of 'the other' view since there is know way to know which view the user is manipulating at the time you update the camera.
To work usefully the sync needs to be from which ever viewer the user is navigating on to all other viewers on the page. Without knowing which viewer is active I am not sure how this can be done. Any ideas? Would be great if there was an event in the API which told us when a viewer got focus. Of course an oncamerachange event would be even better still.
Definitely looking for any creative ideas of how to do this, I think there is something I just haven't thought of.