Yes, something like that will be implemented later.
I don’t think this is a good idea. The general scheme is to allow UI features to be completely visible or completely hidden, with several options for temporarily show a panel. Quibbling over a few pixels by hiding part of a panel is going to cause problems.
Compare your screen shot above with another screen shot you posted - the first screen shot in this thread. They are almost identical, but in the other thread you were wondering where the color well for Display Color had gone. In the other thread the right half of the panel had been inadvertently been hidden by a wide layer name and you needed to drag the panel wider to see the color well. I think partially hiding a panel will lead to many support problems like this.
Currently the minimum width of the right sidebar is fixed to a specific number of pixels that will prevent the contents of a sidebar panel from being hidden. It is not bound to the number of available panels in the sidebar.