The current forum descriptions as detailed in the Entry Hall say that the Mod General forum should be used for mod advertisements.

That being said, once the excitement of the expansion pack has died down the only way the RTW community will continue to grow or even to sustain itself is to have either a thriving multiplayer community or a thriving mod community (and preferably both). Players who stick with vanilla SP will ultimately drift away - probably sooner rather than later - and so its in everyone's benefits to develop their interest in these other ways to enjoy the game.

For news, I personally think it should be a matter of who the target audience is - stuff which is intended to be read by single players should go into the Colosseum, stuff intended to be read by multiplayers should go in Campus Martius and stuff intended to be read by modders (which would include the majority of mod announcements, short of major releases) should go in the modding forums.

But either way, this is essentially a discussion about Org policy which should take place in the Watchtower.