(Forked from bug 21279 comment 33 per Brion)
Per bug 21279, code will be patched so that deleted revisions can be referenced
by their rev_id, and this will work regardless of subsequent delete/undelete
activity. Bug 28820 requests that diffs are enhanced to work using rev_id even if one or both revisions are deleted.
Once this is done, Brion has noted that [[Special:Undelete]] needs "more work for a serious overhaul" (bug 21279 comment 33).
This request is to ask that building on bug 28820, that [[Special:Undelete]] has radio buttons and paging for the list of deleted revisions, so that a user can select a diff between any two revisions listed as is possible for undeleted revisions (on history pages).
At present a diff between arbitrary deleted revisions is not possible, and if a revision is deleted then it is not possible to view its diff against another deleted revision, even if the user has the appropriate viewing rights to them.