Oh thank you for this!
Once this is stable, you can imagine impersonation_enabled_groups and go the other way around: participate as a normal member, and only go to admin whenever you need it… aka sudo mode… It could make ways to change persona on-demand… For example, the Discourse Staff Alias limits pseudo-impersonation to a single team alias, but expanding impersonation, one could be able to change persona according to various criteria…
E.g., a @well-being.team member could post as a group alias to deflect personal grudges, an author could post as @narrator or @characterN to write an interactive story, a teacher could impersonate a pupil to understand her perspective… all according to customizable groups. 
An important feature I guess would be that impersonation sessions are properly logged and known to the impersonated user.