This is great, thank you for taking this importer a step further! 
I do hope in time it can also be expanded to include Tags, if not Attachments.
How much work might it be to add Tag support? I see vBulletin 5 and maybe a couple others have possible models of how it works, but I have no idea how much that would need to be adjusted for Flarum. Thanks for any insight anyone can provide, and no worries if it’s not something that can really be answered without doing it. 