But I know that @bon has been busy with many other site updates and developer documentation always trails a bit.
But from the user perspective you can easily see the results of the improved API. Just compare the settings of themes in RW7 to the those in RW8. RW7 themes were limited to popup menus and colorwells. In RW8 there are quite a few new ways to configure things.
I like to think they took a bit of inspiration from the Stacks API.