I’ve created a Jira issue and I intend to work on this as part of the current roadmap, i.e., for the XWiki 15.8 release. I’ve also opened a vote to reach a conclusion if we actually want to implement this change as so far I haven’t received a lot of feedback.
I unfortunately cannot think of another option to achieve the same. In case you’re not aware, on a (single) page level rights can be managed by anybody with edit right but this is not the same of course as you cannot, say, remove view right for a whole space.