I heard that gwx 3.0 will have a huge net of sewers under the continents, so you can travel around faster.
They will be 100 meters radius so you can maneuver easily inside them, and also they will have lights in the bottom, just like an airport runway, so you can use them at night...
Jokes apart, GWX crew usually don't let go much info on upcoming projects, they like to keep it as a surprise. There's a thread about the 3.0 version, which the few info that leaks can be found. Keep an eye on it!