Once they've stopped patching and adding DLC, I believe Ubisoft could sell at least as many copies as they have to date, by releasing a DRM-free, all-DLC-included "Settlers 7: Complete Edition".
(Btw, the reason I'm in this forum is not because I've bought Settlers 7, rather it's because I just got a refund for From Dust because of the DRM, and was looking for information whether they had removed DRM from their old games yet.)
While as many copies to date may be an overstatement, as a person with 4 computers for LAN play with my wife and our friends, I think this game is a good fit for our group, but will not buy until LAN is an option. That is four copies. I'm sure there are quite a few other folks like me out there.