Once the DLL is released. Modders can't make proper mods until they release the DLL. Civ 4, was released immediately and had an amazing mod community. Civ 5 was delayed release, and the modding community got into a groove afterwards for some amazing mods.

Civ 6, who knows. The longer they wait, they more they have to rely on their game to drive play. And the AI for example, is a trainwreck that needs help