I have to just be missing something here. Why is the "edit domain" option still only available when you have more than 1 active user selected? My tenant has a couple custom domains. Students get one and employees get a different one. When I create a new employee in active directory and adsync runs, the user is created in 365 with their onmicrosoft.com address as the domain instead of the custom one. The only way to change that is to select two users and click the triple dots and change domain. Why can the change domain option not exist when any number of users are selected?!?
I know it sounds petty, but often times finding two users that are supposed to be in the same domain in the sea of people in different domains can be very frustrating.
The option is still there for single selection, just needs few more clicks. I guess they simply don't consider it "frequent enough" to expose it directly as one of the actions on top. Whereas when you bulk select users, the list of actions is limited, thus it gets bumped to it. Anyway, leave a feedback via the button in the portal or post it on UserVoice.