Things are at a point where I think the upgrade can be done. I've done some server and other updates and am now doing some dry runs for updating the database. It's largely the same format as the current DB, but there are some alterations. I expect the entire history -- articles, comments, private mail -- to be ported over successfully. Features I've leaving behind, at least for now, include the ping lists, bozo list, keywords, bookmarks and a few other things won't be ported as I expect they are unused right now. But the data will be preserved for some time in case I do decide to port those features as well.
There was down time today for some of this but I don't expect any more down time until the official migration takes place.