Parallellised windows

I would like to view both windows synchronised or parallellised (NO file transfer, only their display!):

1. same sorting order in both windows, change one automatically changes the other accordingly;
   
2. synchronised scrolling, i.e. always same file on same line in both windows;
   
3. if a file exists on only one side, the other one should display an empty line.
   

Of course it should be the user's choice whether (s)he wants to enable this or not.

Thanks for your suggestion.
We will see, if more people ask for this.