You can use use the arrow keys on your keyboard to cursor through Enum dropdowns without using the mouse. The only downside is having to move your hand to a weird place on your keyboard.
While that is true, this suggestion would provide a better quality of life improvement. The goal of the suggestion was to prevent clicks and easily preview only the values you wish to view. With your suggested method, the preview is only linear and still provides more input than simply hovering your mouse.
The original value is also does not revert to the previous value if you wish to cancel. This would be done by simply clicking anywhere outside of the dropdown menu.