There is always room for more wonders, but I would love an Ethnic diversity expansion with different unit skins for each culture, like in the the existing mod. They could include one extra unique unit or building for each civ and it would be a success for sure. Another expansion I wish for is one with improved trade, where international trade routes were visible on map and could be blockaded etch. The more luxury resources witch is present near city compared to what the trade partner got sets the gold you earn. Id like it if the caravan units was back to set them up. Caravans would have increased water movement. The great merchants could be able to create more or improved better trade routes than the caravan unit. I would also like if they added a slave mechanic since its been a big part of history. Slaves sometimes get captured by defeated units, or taken in barbarian camps. Slave that can act as workers until they perish or join cities to boost production and food. And while they add special city population they should add nobility and religious population as well. Perhaps if you got the right military social policy you can have your fourth level veteran military unit join the city as nobility to get culture, extra unit exp and points for building generals. While the priest population give extra faith and happiness. Another thing I would love would be improved environmental rules like in Alpha Centauri where every hex would have different water assets calculated from things like rainfall (Rainfall being dependent on the distance to the seas/lakes and surrounding mountains) and the vegetation in surrounding hexes. So if you cut down all forests and create farms the water access in the hexes and those beside them will be slightly decreased, affecting the food output or in worst cases creating new desserts. And if you burn down the farms the tiles would eventually have forests growing back like in northern France after the viking plundering the country for several generations. I guess it would be complicating things to much to create different soils its enough to have today's plain, grasslands and tundra tiles etc. You know a big part of the world that used to be green and lush with rich animal life is now desserts or close to it because of what man has done and that is a thing that can create interesting aspects in a game like civ. Please Firaxis take these ideas and use them.