Does no multiplayer also mean no world sharing or component packs?
Im not 100% certain, but given that there will be world transfers from Xbox, this means that the worlds are in a file. As such I would assume you can send that file to someone outside the game, and they would simply add it to their own resource files.
I.E. You send an email to someone with your map file, they add that map file to their own "maps" folder. (correct me if I'm wrong here guys).
As for in game sharing I can't say.