First of all, as I written in the design page, all the other tabs (comments, attachments, history) can change the document. Moreover, the fact that the Information tab didn’t change the document before doesn’t mean it cannot change the document in the future. I don’t see why you shouldn’t be able to modify some of the information related to the current page.
Note that modifying the information from view mode, from the information tab, is in-line with the goal of the 12.x cycle to make XWiki more editable in-place, right from where the information is displayed. Moreover, with the introduction of in-place edit in 12.3 the simple users won’t have access from the UI to the old Wiki / WYSIWYG edit mode so they need to have access to this page information and be able to change it.