I think the reason they don't want to release the dll. is because they know it would hurt their sales in the long run. If they released it, modders would get to work and sooner or later they would have a brand new Vox Populi for Civ VI in the workshop. This wouldn't only hurt their professional image as designers/programmers, it'd mean that, as has already happen with IV and V, many people would choose to stay when VII is released, since VI would be straight up a better product. Even those who decided to buy VII (many of them on discount), could be eventually disappointed with the direction of the new game and return to the old ones for no coming back, so never buying the subsequent expansions of the new. We have a few examples of this in the forum and are totally understandable to be honest. On the other hand, Civ is and always has been a game living off the community and its mods. If they neglect that part of their bussiness because they don't see immediate economic benefit, they will eventually lose the support of their customers. There will be others ready to take advantage of this and honestly, if they don't want their game improved, I'll be on the other boat.