On next Packagekit will have support for unofficial repositories. Like gnome.rpath.org will back the Packagekit.
Im add my personal repo and seen all work.
For problem getting other repos its the generate cache. My personal repo take 15sec get the info and write the xml.
But if you have a high bandwidth its no a problem. It generate faster than me (512Kb/s).
Now its not available for test :P but on next ...