We have pretty strict requirements how the group tags are shown. 
But there are only 2 ways to use it, 1) yast view based on groups 2) using rpm -q to get information for the individual package. For all other purposes from zypp/packagekit this stuff is ignored.
In general it does not really make sense to install packages based on groups. As Fedora already deprecated this tag it would make sense for us to drop it too .
Proposed change would be to kill the Yast UI and then have spec-cleaner to drop the part where needed. It won't break on older releases as it would simply have Undefined as a group.
 https://en.opensuse.org/openSUSE:Package_group_guidelines  https://fedoraproject.org/wiki/Packaging:Guidelines#Tags_and_Sectio ns  https://fedoraproject.org/wiki/RPMGroups