Currently, if an admin goes to [[Special:Undelete]] to undelete various revisions of certain page, he may want to invert the selection of all checkboxes. If he clicks in the [ Invert selection ] button, the page will be reloaded in order to invert the selection.
which is defined at
I think the same idea should be applied on [[Special:Undelete]].
Indeed, right now, there is a gadget on Wikibooks which does exactly that: