Going by what was said on the trem.net thread, I think it's more custom maps and such. So if i make a map, I could sell it for money. Nothing that will effect gameplay.

To be honest I think it's a bad idea. Perhaps things like TF2 hats could work, but asking people to pay for maps will just severely limit how many people will play your map, seeing as everyone would need to have bought the map for everyone to play.