1) allow to "offload" file attachments from FB cases to any repository (by default to Kiln!) http://kiln.stackexchange.com/questions/279/allow-to-offload-detach-and-push-attachments-from-fb-cases-and-case-emails-into and of course maintain a link to the repository committ
2) allow to delete file attachments with deletion comment and timestamp
3) around the ideas 1)+2) consider a periodic maintenance rule to retire attachments (delete or dump to the file system) i.e. by age or any filter
4) well, you might as well then also make it easier to attach multiple files at once :-) , since it would be painless to get rid of them again anytime.
In regards to any serious long-term use of FB for projects more then just a few hundred cases, I find these features essential. It is no practical workaround in a corporate setting to advise administrators to "prune" / or truncate database tables to emulate data rentention policies.