We consider moving quite a big forum to your solution. The problem is that our current engine is 13 years old phpBB with some mind blowing modification on board. I see some importing options in XenForo, but I'm not so stupid to believe it will work with our forum. So could you explain me or provide documentation how importers work? The source code of any existing importer will also be extremely helpful. Then we will rethink if we are able to write one suitable for us, and then we can make a decision of buying your solution.