The main changes were indeed for better Xcode projects, but it is worth noting that the document is completely new. Joseph is completely right though, there's no reason Apple would touch this after 5 years if they weren't working on something!
For me, I'm hoping 4.0 brings some new APIs. I really want custom adjustment bricks or ways to extend some smart albums or stacks.
...Actually, I'd be content if Apple let me re-write a custom auto-stack plugin.