Found stable releases for UIkit 7.x-2.x and 8.x-2.x branches but not the 7.x-3.x and 8.x-3.x branches? There's a reason for that!
YOOtheme still has UIkit 3 in beta and we're not sure when a stable release will be ready. We've been keeping an eye on their blog but haven't heard of an expected release date. But we'll begin getting stable releases as soon as they have a stable release ready.