Trading is dead compared with the second world, look at the current "Apples For Oranges" -Thread.
bring back the "Ring of Brodgar", only for cities with more than 30/40 or 50 members.
made out of a huge amount of cellar stones (boulders), add a new option to these large stones "Extract Boulder"...
and the "Ring of ..." should have no city authority, if people want they have to build banners.
this could bring back teleportation and bulk-trading to the game and is also useful for a big market place with vending stands (if needed)!