This would be really nice to have. I'd like to add that at least the MATE and Cinnamon spins, possibly others, do not include PackageKit and instead expect users to update using yumex-dnf or dnf itself. So ideally an offline update mechanism can be added to dnf, and then exposed in yumex-dnf. But we may have to consider installing PackageKit in those spins. My concern with this is that PackageKit and dnf do not share history and many users are used to using dnf.