If a user installed a fresh KDE on HiDPI devices and boot into workspace, the scale factor is always 1 and panel height is too small. Hope KDE will detect screen DPI and set proper scale factor and panel height, so that users won't need to manually change anything. For example, on a 13 inch full hd laptop, the scale factor is automatically set to 1.5 and panel height is 50% higher.
Wayland does already. On X it's complex.