KenjiTakahashi [1] filed a request to merge sddm-qt5 [2] into sddm [3]: As of 0.9.0, upstream dropped qt4 support. It means that the standard package is qt5 now.
[1] https://aur.archlinux.org/account/KenjiTakahashi/ [2] https://aur.archlinux.org/pkgbase/sddm-qt5/ [3] https://aur.archlinux.org/pkgbase/sddm/
