it would be cool if pressingt Ctrl+s and other shortcuts would work in *both* of split windows and not just the upper/leftern one - depending on which window the cursor is in. It is quite annoying if one always has to select the right source file within the tabs on top of the leftern window just in order to save it.
Enabling a separate tab bar on top of the second window would be even cooler - thus one could use it as a real two-files source editor at a time. I really like to have a header file in the leftern window and the matching source file in the right one.
If split window mode is getting disabled the tabs could just be moved together in one bar again and on splitting up they'll all remain in the leftern one.