We implemented the C3 superclass linearization algorithm in the Open Dylan compiler. This is more intuitive in some corner cases, and allows further performance improvements, especially compression of dispatch tables. It has been merged into the opendylan GitHub repository and will be the default in the next release (2012.1). A serious warning will be issued if the new C3 linearization is different from the old linearization specified in the DRM.
Further information is available in the accepted Dylan enhancement proposal here.