FYI, we recently published a paper on IPv4-IPv6 handovers based on HIP:S. Varjonen, M. Komu, A. Gurtov, Secure and Efficient IPv4/IPv6 Handovers Using Host-Based Identifier-Locator Split, in Proc. of The 17th International Conference on Software, Telecommunications and Computer Networks (SoftCOM 2009), 2009.