CyberGene Is it possible to have separate file size limits based on the type of file? Because I have a music forum and people attach audio files and I have increased the file limit but then it also applies to images and I don't want people to be able to upload huge images
Not possible right now. Like the idea, this could be build.
CyberGene Is it possible to have a quota per user, e.g. to limit the total upload size per user per day. Also per post? Per discussion? Maybe a group based permission
Not possible right now. Like the idea, this could be build.
CyberGene Is it possible to limit/disable the upload in private discussions
Not possible right now. Like the idea, this could be build.
CyberGene Is there an easy way to see stats, such as a sorted list of users by their total upload. Also separated by private discussions
Not possible right now. Uploads are connected to users though, it could be build.
CyberGene Is it possible to see the stats of the biggest files, as well as last accessed, total number of downloads, etc. For instance I would like to be able to delete files that have been uploaded long ago and are not accessed anymore.
Not possible right now. I think should be possible, but it might be a bit resource intensive, so probably this should be moved to a background task. Could be build.
CyberGene Is it possible to list files that are not referred to from any discussion/post? Also files that were never accessed?
This was on the roadmap, it could be build.
CyberGene Is it possible to see a list of all the uploaded files and the corresponding posts that link to the file?
This was planned, it could be build.
CyberGene Is it possible to delete the actual files?
This was planned, it could be build.
All the features you mention I like. But our time is limited and extensions inside the Friends of Flarum namespace are meant to be maintained. Active development on those are usually commissioned or based on need of people able to develop and then contributed.
If you would like to commission any of these features, make sure to take a look at https://flarum.org/partners for recommended developer parties.