We have Paid Seat Groups established, and have an internal policy that all licensed users need to belong to a seat group. However, we still have admins who forget to add this because they aren't promoted for it when adding a user from products>users>add user>existing users screen. This results in a Paid Seat Group admin thinking they have seats available, but there aren't any because seats were assigned without a group.
Thank you for your idea. It is required for paid seat group owners who are not billing admins to select a paid seat group when adding a brand new user. It is unlikely that we will add the option to select a paid seat group for an existing user in Products > Users. This is because existing users could already be in a different group (that the paid seat group owner may not have permission to update) they could unknowingly move the user when they should not.
One option for updating existing users would be to filter the Settings > Account > Users page to show users with no group and then bulk edit.