Currently Koha's ILL module allows for the Koha library to be a borrowing library/institution but does not currently allow for the Koha library to be a supplying agency/lending library.
Interested! I still need to have a conversation with a library about this, but I think they're interested in using Koha to manually track ILLs which they process via other external systems/processes. I'm going to look for confirmation on that though...