Balancing is one thing. It's always possible to nerf it so hard that it doesn't become overpowered. The main question is, does it actually provide good gameplay?
This feature is requested by fans on a thematic basis, but giving players this tool will devalue the importance of city placement and tiles. There's good gameplay reasons for keeping that 20-cottages-city low on production.
To me it's a bit like the request for setting science slider individually for each city in Civ4. Sure, it would be very convenient for the player, but it would destroy the game.
This feature is requested by fans on a thematic basis, but giving players this tool will devalue the importance of city placement and tiles. There's good gameplay reasons for keeping that 20-cottages-city low on production.
To me it's a bit like the request for setting science slider individually for each city in Civ4. Sure, it would be very convenient for the player, but it would destroy the game.