My only fear is there is the possibility of fracturing (too strong a word) of the modding community. I have found that the more we can all agree on maintaining and posting in the same place, the easier it is for everyone. I kind of dislike the idea of posting and updating things here, then on the Nexus, then the wiki....then in the workshop. I'm lazy.
That is a slightly valid concern. With different platforms/versions/websites all selling the game and hosting mods, Steam workshop (unless it's not implemented for some reason) is going to have a big community, that's a given. Nexus will probably be substantial as well as some people prefer all their work be uploaded there. The Wiki, of course, but for a wiki unless the mods are also "hosted" on the wiki, I'd expect more of a list to mod pages.
I would always expect a master list of the best mods and active community of those modding the game to be on game's official forums though. If I want to look for other modder's work or other modders to work with, I always find them on that game's site. I would expect other than the odd modder doing something on his or her own most modders and those looking for mods will probably come here as well. The only time I've ever not gone to a game's site and found a mod was on the Steam workshop. Every other mod I've used I found through that game's site, even when that game sent me to the Nexus. I imagine that would be the case with most, but, I might either be giving my-self too much credit or not giving everyone else enough. Maybe more people do go straight to sites like Nexus before going to a particular game's site these days. I can really only speak for my-self personally and my own experiences finding mods.