How about adding/changing some wonders so that they function as a unique district giving special bonuses. How about the Great Library being a unique campus districts giving the same bonuses as it does now + the usual campus + library yields. Maybe have different/no adjacency bonus though. Later you can put a university and a research lab inside the GL, too. This could work for many other wonders as well.
Quite some wonders come to my mind that could function as districts. Göbekli Tepe could make a nice Holy Site, the Grand Bazaar of Istanbul could be a commercial hub giving bonus on trade routes from that city, Krak des Chevaliers could be a unique encampment and so on.
Of course, having a wonder functioning as a district would prevent that city to build the normal version of this district and the other way around: a city with the GL would not be able to build a normal campus any more. And district wonders would not count towards the district cap.
Quite some wonders come to my mind that could function as districts. Göbekli Tepe could make a nice Holy Site, the Grand Bazaar of Istanbul could be a commercial hub giving bonus on trade routes from that city, Krak des Chevaliers could be a unique encampment and so on.
Of course, having a wonder functioning as a district would prevent that city to build the normal version of this district and the other way around: a city with the GL would not be able to build a normal campus any more. And district wonders would not count towards the district cap.