Back from his vacation, Epic's Brandon Reinhart updated his .plan with a general update on the Linux port of Unreal Tournament, which he will be making open source according to the Artistic License (they can't release it according to the GPL, as this is just the Linux part of the engine they're releasing). It's a big update, but here's a brief excerpt with some details:

I'm back from visting relatives and I've been rolling on the Linux open source stuff. I've got my project approved with Source Forge. Once I get everything set up, I'll announce the URL but I'm sure the sneaky will be able to find the page.

I've chosen the Artistic License. I feel that it allows mod developers a lot of freedom with the open code, while not putting Epic into any weird positions with the undisclosed part of the engine.

I plan on open sourcing the following libraries:
XDrv
XMesaGLDrv
GlideDrv
Audio
XLaunch

In addition, the release archive and rcs will include the public headers for the other engine libraries (core, engine, etc). Some of the above libraries compile both under Linux and Win32. I'll write up some specific guidelines for contributing authors. For example code that is contributed to the GlideDrv library must compile under both Win32 and Linux.