Hello everyone,
Is this the Brian whose wife just had a baby or another one?
Yes I am that Brian :)
Is there a design doc? What is the status -- is there a GUI or just the network protocol? Is there a server side where people can find each other, or just peer to peer?
Not really, but if you look in the torcs-ng-devel archives in the very early messages.  You can get a rough idea of my approach. 

Currently it is a very simple system.  Someone hosts the game and the other players type in the ip address of the server to connect.  It is a very basic lobby system.  There is no reason that a nicer system could be added later.

Is the code in the torcs-ng svn? I don't see it in trunk or in any of your branches. We'd also love to take a look at what you've got.
No it is not checked into torcs-ng svn.  It is currently on my computer.  The code still needs polish and is missing needed features.  I wrote my code based on sdl-port back in early decemember.  If you guys want I could upload my src folder in a zip someone.  Currently it only compiles on Windows and you need to add the enet library to cmake.  I don't exspect major problems moving it to Linux.