Hi,
L4.sec is (and probably will be for quite some time) an experiment that
is still worked on in our group. Mainly due to maintenance and support
issues the sources have not been officially released yet. Our roadmap
regarding L4.sec is to continue experimenting with capabilities and user controlled kernel memory management. Some of the results we already integrated into the Fiasco kernel, which is our mainstream kernel as for now. These include kernel memory quotas, security monitor style IPC permissions (though no local names yet).
Others are likely to be integrated in some form in the Nova microhypervisor, which we are currently developing in the course of the Robin project.