Andrew Pollack has published a paper overviewing the new Domino Designer 8.5 XPages development construct. Originally written to be published on IBM's site, he's released it now as a PDF with IBM's permission.  This PDF is worth a read if you want to understand new capabilities coming in Domino 8.5, as well as a higher-level thought about the future of Domino development.

The PDF file can be downloaded here .