Please add arches when you think it is ready. I understand it is more like something broken out of dev-libs/weston rather than completely new. KDE Plasma 5.23.5 is already being stabilised and referencing the package in pkg_postinst optfeature, so having it stable too would be more elegant. Plasma is stable on amd64, arm64 and x86. dev-libs/weston is stable on amd64, arm, arm64, ppc64 and x86.
Adding arches according to Plasma stable keywords. Maintainers, you may add additional arches as you see fit.
amd64 done
x86 done
arm64 done all arches done