About the interesting Aubrey's onion model, I just discovered basic AJAX tricks, they are great do change the contents of a page using data stored into different pages and/or javascript variables (as wgUserName) and/or preferences or gadgets.
So, I'll think a little about a "AJAX onion", that would allow to save "leaves of onion" in different pages, but consider that any dinamic change of rendered HTML is visible only to user and there's no, or few, trace of them into wiki code.
Just now, servers seem down, so I cant test what happens saving a HTML page whose code has been manipulated via AJAX, I presume, any change will be saved, but I've to test to be sure.
Alex