The x11-misc/sddm ebuild looks like this: IUSE="consolekit systemd +upower" REQUIRED_USE="?? ( upower systemd )" To avoid hitting the REQUIRED_USE, I suggest masking the upower USE flag in the systemd profile target.
Full message: These are the packages that would be merged, in order: Calculating dependencies... done! !!! The ebuild selected to satisfy "x11-misc/sddm" has unmet requirements. - x11-misc/sddm-0.11.0-r1::gentoo USE="systemd upower (-consolekit)" ABI_X86="64" The following REQUIRED_USE flag constraints are unsatisfied: at-most-one-of ( upower systemd )
@Jonathan Vasquez: I can't follow your comment. @Michael Palimaka: I do not remember now what was ther reason for this USEs being mutually exclusive, I need to recheck it.
I removed upower USE from ebuild. It depends on upower when !systemd now.