I suggest to provide non-global rename / stewards limited access to global rename requests.
For Special:GlobalRenameQueue/request/* we generally use this a reason in the summary, therefore limited access for "non renamer" would be helpful
For example:
From FormerUsername To: NewUsername Status approved Requested 06:15, 22 June 2015 Completed 06:25, 22 June 2015 Done by Renamer