This is a nice start, but I already see one issue with this that the "Navigation popup" doesn't have: nothing on the hovercard is clickable, and thus you can't go more than one level down a tree.

The navigation popups are great except that if you move the mouse off them then they close, so as you traverse down the tree you lose parents. And you kinda end up with the same issue as before only now you really have no idea how you got there because you don't even have the open tabs to guide.[0]

[0] http://imgur.com/RS0IEet.png