Open Source Web Processing Versus ArcGIS Server

James Fee looks at Christopher Schmidt's WPSServer and writes:

Now this of course won't replace the complex analysis that ArcGIS Desktop or even ArcGIS Server can accomplish, but why not use such lightweight tools for lightweight needs?

A RESTful web geo-processor that provides a DSL for describing complex processes and analyses (my preference would be for Javascript ala CouchDB, and I'm hoping to find funding to develop such a thing and make Mush a more powerful tool for the digital humanities) and lets users create new processing resources from these scripts could certainly begin to replace ArcGIS Server. I'm a regular user of open source software that generates Python workflow code from UML, and I can imagine something like ArchGenXML coming to the aid of people who like to draw their processes graphically.