I have few usability related questions to see if such things would be possible in Qubes OS.
Would it be possible for Qubes OS to implement similar window maximization as one can see in Ubuntu?
That is, when a window is maximized then its title bar integrates with the toolbar.
Edit: Also would it be possible for applications to enter into full screen mode?
However, if you want, you can still manually put any window in proper full screen mode. It's just a right click away, at least on XFCE.