jack-strap
Transferring files between users (ie: a student sending a draft of his thesis to his supervisor) is normally handled by email, and for large files, this can become a problem. First, most mail exchangers implement limits on file sizes. Second, the receiving user doesn't always delete the email, taking unnecessary space on the mail server.
To overcome this problem, dokuwiki users could, via a plugin, send files to each other, send files to external users (making use of "tickets"), or request files from external users (also by using "tickets").
Files thus sent could be deleted automatically after 1) a certain time limit, or 2) some time after being downloaded successfully
Tickets could allow access for external users to a normally acl restricted system, with some "number of use"/"time of use" limit on a ticket, etc.
File requests/ reception notification could be handled by email for external users, or through a special page in dokuwik / under the user page namespace for exemple.
It seems to me that the functionality, at least for handling file transfers between registered users, would be easy to implement using "distributedACL"... but I'm not too sure where to start with writing such plugin.