*** Fearmonger Alert ***
It's even worse than that... Most companies "OWN" all modded content created by modders. If 2K Firaxis becomes one of them (if they aren't already; unknown here), they could Sell content as DLC that users create! And it would not be required to pay the modder anything, and the modder would no longer own their creation (which they probably didn't to begin with).
Will it happen though? Probably not.
I think that is already the case.