In the moment the player window is fix in the middle of the Shotcut GUI.
It would be nice to have both as dockables.
So the user himself can make a tabbed design,
but he also can have the two players side by side.
Not everyone has screen real-estate to accommodate this comfortably and would mean reduced ‘player’ sizes which I don’t find very useful.
Personally speaking, the current UI arrangement is fine (and I use 24" 16:10 ratio screens)
Yes, if the two suggested dockables would be dragged to tabbed design (this may be the predefined design), the only difference to now would be the little dockable controls in the right upper corner.