i think a great feature would be a Z axis view. ie: from the front view you could rotate only in the Z axis with RMB this way you could stay in ortho looking at ZX but you wouldn't be limited to only looking at 90 deg. increments of your model (front, back, left, right); maybe a degree indicator in place of the viewport title, with 0 deg. being front 180 being back etc. With RMB you could rotate the view and see the title update with snaps every 90 deg. Could also be done in top view with Y axis . Image the freedom and accuracy this could add to modeling. you may never have to switch in and out of perspective again. Could be a revolutionary concept in 3D modeling think about it.

What do you think?