"Since the new system only allows one user per name, there are some cases where accounts will need to be renamed."
What a horrible idea. I sure hope that's not what unified login will actually be.
There is no way you could have unified login without renaming accounts. If two people currently have the same name on different projects they cannot both continue to use that name after unified login, thus at least one of them must be renamed. (The one with the least edits is the plan, I think.)