I believe it's possible to run a migration script as an "append" instead of a "nuke and replace".
You'll have to ask @akhoury more about that, unfortunately 😦
Having visited NodeBB from work, imgur appears to be blocked behind the corporate firewall. Would it be possible to implement some form of backup in case of this, as it can make the site look quite bland when there's no pictures etc. I know self hosting avatars is an option, but for admins that want to use imgur, but may have imgur blocked.
I should probably add, I'm an admin on this system and can get around it, but that's not the point.
Should be pretty easy to build a backup system. Imgur is just a handy plugin to send images there. Every site that uses a CDN has this problem, potentially. A plugin to upload the images locally or to S3 should be very easy. Very few people want to use locally hosted images, though. But for those that do, the option would be good. Then blocking would be uniform.