I have noticed, that I can currently change the URL/slug of a published page by creating a new draft version and then changing the slug in the page settings. There is no need to publish the draft for the change to take effect on the page.
I would expect it to only change the URL once I publish the draft version with the changed slug.
Otherwise I would expect to change the slug field anytime without the need for a new draft version.
cc @fsbraun