I think I remember in old slsk there was possibility to provide a upload slot in upload window to a chosen user.
For example you have limited upload slots to 2 and currently 2 users are downloading from you. A friend asks one file from you and queues it. Even your 2 upload slots are used by other users you could provide additional slot to your friend by clicking on username and choosing "force upload" or something like that.
Maybe that would be a good feature to add?