5-6 million seems the most logical one to me, though it could be a bit lower then 5 million. All the freshness has worn off by now and I don't see many people logging in unless there's a raid going. Realm activities seem to be going down a lot aswell, and most of my friends who came back for Legion have been long gone after a month or two. They did like the expansion for most of the part but there's just little reason to keep subbed and do the same content over and over again.