There are no current plans to migrate any content.
Unfortunately people jumped the gun on launching this somewhat and OWG didn’t have a chance to revisit the question of what if any data should be migrated - we have discussed it in the past but it was quite a long time ago and I can’t remember what conclusions we reached.
That was purely about osm.org content though - stuff from forum.openstreetmap.org, help.openstreetmap.org and lists.openstreetmap.org. I don’t believe we have ever considered bringing in content from third party sites.