Thanks for the tip on the 'Zoom area' tool. i'll try that.

I'm not sure what you mean by:
"The method you're describing would not be a great fit with MoI because you wouldn't have a chance to use object snap to precisely set the target point."

Because in the method / demo I uploaded I'm not snapping to anything. Snapping is not active at all. It's simply that the intersection of the 'cursor ray' and face of first visible object is automatically used to establish the rotation / zoom origin. For the user it's simply a case of position the cursor over the scene and Alt drag.