It is true the right gutter's general scrolling window view capability no longer exists in 4.0. However, if code errors exist, then small blue squares (uncompiled code) or slightly larger red rectangles (compiled code) appear in the gutter representing the relative positions of the bad code. Hovering the mouse over those produces a pop-up display of the offending code and, in fact, the pop-up will not display if the Ctrl key is pressed at the same time. Of course, clicking on the rectangles or squares moves the editor's current line to that code as in earlier releases.
So it is not clear whether this is merely the new, intended behavior, or if more of the prior behavior remains to be implemented in 4.0. As far as I can tell, nothing important has been lost here, but that is just my opinion.
SQL Developer Team