Finally, we have progressed, took this long to get the test migration to work. ( I got Xenforo the day I said something)
Depending on the situation, and I will make several full posts, the site will be down anywhere from 1 to 2 days for the change over to Xenforo.
Unlike all you super smart, know better than everyone else, these things don't just "happen", there is no clean install when you have years of data. (Unless you want to lose 100% of everything) The migration tool was only in beta for vBulletin 5 and our upgrade paths are/were not so simple. So they developed the beta tool on the fly and believe they have it ready to roll out.
Once I get the details and know definitely what path we are taking, this should start to roll very soon. But we will be offline for the upgrade, potentially several days.