The most recent FreeBSD progress report is out; among other things, it talks about work on multi-IPv4/IPv6 jails, TCP cleanup, and TCP reassembly optimization.   Interestingly, I think there’s related work in DragonFly - the DragonFly jail changes were about a year ago, and Jeff Hsu’s work on the DragonFly network stack seems similar.

I doubt there’s many people on the planet with the brainpower and time for this, but it would be interesting to have a large-scare compare/contrast of the different BSD styles for solving problems in code.