sys-apps/portage-2.3.0 cannot be built with USE=selinux and PYTHON_TARGETS=pypy, because that creates a dependency problem related to sys-libs/libselinux-2.5-r1, which does not support PYTHON_TARGETS=pypy. My wish would be for sys-libs/libselinux to gain support for PYTHON_TARGETS=pypy. Otherwise sys-apps/portage would at least need REQUIRED_USE="selinux? ( !python_targets_pypy )".
The SELinux profiles mask the python_targets_pypy flag for portage, and all non-SELinux profiles mask the selinux flag, so this isn't an issue (anymore?).