Improved trackball navigation

Hello,

I prefer to use the trackball navigation however I always felt like there is something wrong with the one in Blender. I try to describe the issue below the best I can.

Let's start with the goods of the current state:

The trackball navigation works as expected as long as you have something selected and you have framed the selection or Orbit around selected is enabled. The navigation rotates properly around the object in these cases.

The trackball navigation works semi as expected when you pan around and nothing is selected as long as you don't zoom.

Trackball navigation does not work predictably when you have nothing selected, you move your camera away from the last selected object and do any zooming. Alt + Middle mouse click anywhere in the scene and it will lose the sense orientation completely so it will be hard to understand which point the camera is pivoting around. Moving around the scene like this would be useful when working on a big scene with multiple objects.

Expected behavior.

1. When nothing is selected trackball navigation should rotate around the center of the view. Even after you zoom. (I think this is how it works in other packages like Modo? Correct me if I am wrong)
2. When Alt + MMB (Center view to mouse) the trackball navigation should make the camera rotate around the mouse position.

Attached video below to describe the issue. As seen on the beginning on the video the trackball navigation works on the first two examples. Once I do a small zoom in and out it seems like the system looses its orientation.