At this moment you can only set up an interliningagreement that is active over the whole world. A problem in my opinion is that they can be realy expensive if the two airlines have a lot of airports they connect.
For example if I had an airline in AMS and wanted to interline with an airline with his hub in JFK I only want the possibility that pax can transfer at JFK and AMS, not in for example ATL, BOS, FRA, LHR, CDG or MAN just because we have both a spoke from our H&S-system in those places.
What I would love to see is an option that I can select the airports where a transfer between the two airlines is possible. This would probably sink the cost of IL-ing making it more attractive for young airlines to interline with a major airline, secondly (I think) its less stressful for the servers because a lot of ORS options will not be existing anymore.
I hope my point is clear, since English writing is not my best point.
Looking forward to see your thoughts on the subject.