I am looking for this feature as well. I converted from SMF to XenForo through phpBB3 (site is not live yet) and my thumbnails look off. Would like to correct them.
Is there any chance that you will provide us with an option or a tool to rebuild thumbnails for attachments? Maybe there are any script which can make that. I have same problem like Cujo, after migration a large part of thumbnails looks awful.
Can this realistically not make it into 1.2? Rebuilding attachments and avatars are a huge deal. Especially since most of your customers are coming from other forum software.
No, I've been super busy. It's on my todo list but I'm not sure when I'll get to it. To be honest I think I want to rewrite parts of it if I'm going to release it, as it comes with a few caveats and was written specifically for my use case.
Attachment thumbnail rebuild
Attachment thumbnails can now be rebuild via Tools > Rebuild Caches. This is generally only needed if you change the attachment thumb size.