It is very likely I will be moving my forum from Xenforo to Flarum in the future. I thought I could come up with a list of suggestions.
Threads, forums and prefixes:
I've got 15k threads spread across around 50 forums/subforums. Some of the forums use prefixes.
I think it would make the most sense if all of the above would be treated like tags and the importer would ask about tag assignment for each forum and prefix.
Media sites BBCode:
I see that Xenforo automatically converts YouTube links to something like this: [MEDIA=youtube]7jruQfFUcm8[/MEDIA]
EDIT: This is working correctly!
Media Sites s9e add-on for Xenforo is also available for Flarum. Perhaps that would somehow help with the transition?
Attachments
Attachments are standard Xenforo feature. Importer should be able to convert them to attachments used by appropriate Flarum extension for attachments. HTML5 player for MP3 attachments would be very helpful, but I understand that this is rather a suggestion for an extension, not for the importer itself.
User fields
User custom fields, signatures, profile posts - they don't have corresponding fields in Flarum yet. What about those?
Private conversations
Once they are available I guess they will be included with the importer.
Alerts
History of Alerts could be converted to Flarum Notifications.
Thread URLs
This one is going to be tricky. An ability to keep old thread URLs working.
XenCentral Trading System - feedback for classifieds
Very important for my community.
Xenforo Resources
I use this as articles section. This could be converted straight to Flarum discussions.
Very likely I missed some important points, but that's the list that came to my mind.