I'd like to see something similar in XF.
For example, say you're the admin of a forum and as well as your own personal forum account, you may have a separate account for making admin posts.
I'd like to see the ability to "decide" which profile I am (as admin) posting as. I have a default, i.e. me and a secondary profile. Any forum-related notices are made using the admin profile and everything else is posted under my personal profile.
Right now if I want to make any posts as admin I need to log out of my personal account, sign back in, make the posts, sign out and log back in again.
Multiple profiles/identities would be pretty cool I think.