I would like a CMS that separates the application from its Content.
Ideally, each page would be a separate XML file (or stored in an SQL table I guess) that lives in a Content folder.
This would allow you to easily move portions of a site or the entire site itself with a simple drag and drop operation.
Site builders would have a choice of an online editor, a stand alone local editor, or manual editing of the XML files.
The stand alone local editor would allow you to grab one of the XML pages, edit it and put it back on the site.
The application would be capable of "compiling" the resultant output pages any time a new XML page is dropped in the folder (or updated) to increase performance. So no database accesses or XML I/O would be required to serve the page, only a thin security layer would be used to ensure the user had the proper permission to view the page.
A web service would allow users to programatically upload/download/delete pages.
The site would be able to view the content using different forms, be it a web form, silverlight, or flash.
Widget/Module data would be stored in the pages XML file using a standardized format. The site wouldn't blow up if a widget wasn't installed, it would just decline to show the module or just show the raw XML.
The site would follow vendor standards for skinning (ie, themes).
The stand alone editor would be available in different platforms like Windows,iPhone, Mac, etc.