And this is the right way IMHO. As long as you authorize the storage group, then whoever needs permission for mounting external drives is added to the group.
This method is for actual multiuser systems, that different users are different persons. For actually single user systems, there are many methods to do it.
So I guess the question is, how can this be done without me doing anything (applied from a distro)? A polkit rule sounds good. But still a (lazy/not-real-arch) user needs a HUGE informative banner… 