Since the ncurses-6.0 ebuild doesn't actually install anything,
if it happens to be installed (or re-installed) after
ncurses-6.0-r1 then when the slotmove is applied it will
cause ncurses-6.0-r1 to be autocleaned by emerge as follows:
>>> Auto-cleaning packages...
sys-libs/ncurses
selected: 6.0-r1
protected: 6.0
omitted: none
All selected packages: =sys-libs/ncurses-6.0-r1
move kde-plasma/kio-extras kde-apps/kio-extras
slotmove =sys-libs/ncurses-5.9-r3 5 0
slotmove =sys-libs/ncurses-5.9-r4 5 0
-slotmove ~sys-libs/ncurses-6.0 5 0
move kde-base/baloo-widgets kde-apps/baloo-widgets
slotmove =kde-apps/kde-base-artwork-15.08.0 5 4
move x11-drivers/radeon-ucode sys-firmware/radeon-ucode