The SP campaign thing sounds plausible, KF was supposed to have one back in the mod days, though it never amounted to much, so i could definately see TWI wanting to make it, and perhabs charge a little bit for it, and such a thing would be an optional extra, not something people must have to play online, so it's not unthinkable by any means.
But i just don't see them charging money for normal patches and content updates, that's just so far removed from their buisness model, infact it's the exact opposite of what they wanted to do with RO, and the RO model was a big success, so why on earth would they throw that away?
But they could also be using this DLC section for the upcomming mapping contest, it would be a very smart way for them to make the contestant maps avalible for download and evaluation (without forcing people to download them all which the current patch system would do), very similar to what Epic does with their MSUC, just using Steam to host the files instead of something terribad like Fileplanet.