So if you missed GameTrailers TV, check it here
http://www.gametrailers.com/gametrailerstv_player.php?ep=10&sd=0 (skip to chapter 4 for TF2 stuff)
From the brief flythroughs they showed, here's how Goldrush seems it will work.
First of all, of course, there's the minecart, which blue has to escort through the map. Along the way there are three control points, A, and B, and C, which is the finish.
I'm guessing once you get the cart to A and B, blue respawns faster/further ahead.
It's a very narrow map in some places, and Red has many windows and side routes to hide in.
The end of the map looks similar to the last CP on the 3rd part of dustbowl, with all the buildings around the point, and I think I saw an underground part like on dustbowl.
Looks like it's gonna be fun, and this means that the map is practically finished and ready to be released.