Community Creation in boardgames?

In video games we are seeing emphasis on games that enable community creation that in turn contributes to the enjoyment of the rest of the people who play the game. This has existed for a very long time in the form of mods and variants, but it is now "institutionalized" in games such as Spore and Little Big Planet; in fact, in the latter it appears to be much of the point of the game. The creators of these games have made it very easy for players to create additional "content" that can easily be used by others, even more than the scenario editor in Civilization games or the level editors in shooter games such as Unreal Tournament.

This is a form of "crowd-sourcing", using non-professionals to provide content sometimes as good, or nearly as good, as professionals can provide, but at no cost. Video game companies simply cannot afford to create the vast amount of content gamers now expect, yet gamers want it for no additional cost (complaints about the $60 standard price for video games are common). So they're finding ways to have the fans create the additional content.

My question is, how do we incorporate such "community creation" features like modding/creature creation into boardgames? Collectible card games have something like it except it's all publisher-created. RPGs have had it (all the D&D monsters, classes, adventures) since their beginning. Diplomacy has it in the hundreds of variant created over the years. Some wargames have it in additional scenarios created by fans. But is there a way to make it part and parcel of a game or of gaming?

How do we get something that supports the game and is created (and distributed free) by the fans, the players? BGG is as close as we get, generally, but how many players come to BGG on a regular basis? Not many, really.

Well, if I knew the answers, I wouldn't be asking the question.