Digg had a link to empiresmod, a RTS mod for HL2. I only see a few in-game shots, I’d guess that it still needs some work. Creating a UT Onslaught clone isn’t easy.

The mod looks like it has first person (on foot) mode, in tank (or vehicle) type play and an overview (deploy and plan) screen. That leads me to believe it moves in the direction of the older title Battlezone2 (1997 I think?). I wouldn’t mind if it was like Battlezone2, that was a great first-person RTS. It’s just a bit dated now.