OK, after finally finding the webvr xml in the 1.19 beta I see it looks like view limits are supported, but you need to add them in the webvr xml not the main "tour.xml" as it seems any limits set there are not transferred when the view mode is changed.
I would guess that that is true for all view mode changes.
OK, looks like I'm wrong, I see no way to add view limits in stereo VR mode. The limits I saw in the VR example only apply to the intro VR, not the stereo VR mode.
It seems there are no controls at all in stereo mode, can't zoom in or out and no view limits. Too Bad.
I have an experiment with limits in VR mode, but is less than ideal solution. If you are using 180 ° images just keep the other 180 black, it would be better, and you have some room for interface