The idea of having an XML document that resembles a static map, but also has links to dynamic geographic and multi-media content is not new. Around 2000 to 2002, OGC worked on strategies for drawing and writing on imagery, and encapsulating geodata along with geo-referenced notes, emails, web pages, etc. These activities produced documents on XML for Imagery and Map Annotation (XIMA) and the Location Organizer Folder.
For various reasons, this work lay dormant for a long time. More recently we put together an XML document format for saving the state of Web Mapping Services–their layers, styles and extent. This is called a Web Map Context Document (WMC) (also check out the XML examples here). This was well-received, and led naturally to the desire to reference more services, like WFS and WCS, in there as well. This more powerful document is being called the Open Web Context Document (OWC).
So somehow the ideas behind OWC and KML have some kind of future together. Probably in a suite of versions. Someone recently mentioned the idea of having profiles of KML–small, medium and large perhaps. Small might be for web browsers, medium might be targeted at thicker clients like Google Earth, and large might be the full-powered, OGC service enabled version that the professional GIS community gravitates to. Only time will tell…
Small was meant for mobile browsers like GMM, but all of this is still evolving.