Hi Michael,
Can you implement vewport rotating snap? If you press shift and rotate viewport it will snap to close view for example right and goes to ortho view. Then if you start rotate (may be with presed shift) it will back to perspective 3D view.
Hi Andrei - I think it would be difficult to do the switching between parallel and perspective part of what you're asking for. Those are fairly different types of viewport projections and it's kind of difficult to try and make a transition between them like that.
It might be more possible to do some kind of snap that only does just the view direction alone and not also change the projection like you're talking about.
