After finally updating to 2.13 I noticed the new call script function, very nice, but how about a few more, currently you can call a script when done, how about once seeding is complete and/or once it's been removed from the downloads list. Then all you need is a few scripts (that anybody can make in applescript or automator) and you can completely automate your downloads. (I guess you'd need an option to remove a torrent from the download list once seeded, but that can be handled from the web UI or even from one of the scripts (if transmission is applescript-able, I haven't tried).
And while your in there if you feel the urge you can also add a script to run when the file is added, but that one is probably not very useful.