While the Observer and Sender components mentioned in the source-framework serve valid use-cases, I think they should be separate from this library as they are not crucial for ResourceSync.
This will help us focus the library development on ResourceSync and will probably be easy for us to maintain the code in the long run. Especially with all the various possibilities that could be implemented for the Sender module, along with all the security implications that we have to worry about, we will be entering a rabbit hole.
@dans-er, @giorgiobasile: Thoughts?