Note: originally reported as bug https://developer.blender.org/T64435, but rejected by Brecht as it was considered user interface feedback.
Dang, as “new user” I can’t add more than one image in a post (I have 4), so see the linked bug report for the details.
Edit: finally got restrictions lifted, posting images here after all:
This might be more of a feature improvement than a bug, but in 2.7x whenever the sidebar was shown with N in quad view the whole 3D view would become smaller to accomodate for the sidebar:
In 2.8x, with the sidebar being drawn on top of the 3D view this is fairly suboptimal, as in quad view mode the views become quite small, so the sidebare overlaps a sizeable portion making the two right-hand views much less usable:
Making the sidebar less wide is only possible so much, as it loses its use when becoming too narrow. And hiding the sidebar completely when working in the two right-hand views is not always what you want.
Actually, the above also applies to the toolbox on the left, but to a lesser extend.