There is at least one open source WCMS that uses static export at its core: http://openengine.de/ (site is in German, but docs are in English) - unfortunately, it has been unmaintained since 2010. It will export .htm or .php files depending on whether you need pre-processing on every request.
As far as I know, though, Publicis still use a closed source version of openEngine (openEngine Corporate ASP) for two clients: http://www.siemens.com/ (pretty big fish) and http://www.man-finance.de/ (search for "openEngine" in the source code).
There is at least one open source WCMS that uses static export at its core: http://openengine.de/ (site is in German, but docs are in English) - unfortunately, it has been unmaintained since 2010. It will export .htm or .php files depending on whether you need pre-processing on every request.
As far as I know, though, Publicis still use a closed source version of openEngine (openEngine Corporate ASP) for two clients: http://www.siemens.com/ (pretty big fish) and http://www.man-finance.de/ (search for "openEngine" in the source code).
So this is definitely viable as a core approach.