Hi Ricardo!
You're right, only System Admins can impersonate a user (and you're also right that there would be a privacy issue to discuss, but let's say for emergency maintenance purposes it's perhaps acceptable...)
In fact, if a Domain Admin needs to modify an option for a user who is not present in the "Domain Settings" panel, currently the only possibility is to Login in the user's place.
Now, leaving aside privacy issues, there are 2 ways to do this:
1 - enable Domain Admins to see user passwords (...yes, I know, Privacy!!! I advise against it...)
2 - a Domain Admin can set up a temporary password for his users so that he can perform emergency access WITHOUT knowing the user's REAL password (and clearly without changing it).
In this case, therefore, there are fewer privacy problems.