app-portage/gentoolkit only considers profiles/arch.list from the 'gentoo' repository, but it should also search for arches from profiles in other overlays.
This might be useful when porting Gentoo to new architectures not listed in the 'gentoo' repository. When using an arch not listed in the 'gentoo' repository, ekeyword currently errors with:
$ ekeyword -n myarch /usr/portage/sys-devel/gcc/gcc-8.2.0-r4.ebuild
usage: ekeyword [-h] [-m] [-n] [-v] [-q]
ekeyword: error: unknown arch/argument: myarch