Few things increase the commercial life of a product as much as proper post-release support, and few forms of such support are as cost-effective as harnessing the creative power of the player community. Since scenario play is the core of BoW, more scenarios is more, and it's something the player community should be well capable of giving a hand with.
Would FFG be willing to give some kind of "official" support to community scenario-making? Hosting fanmade scenarios (evaluated for goodness, of course) in the support section of the BoW webpage would be a natural way of doing it. Though, it would be neat, user-friendly and consistent to have the scenarios in the same graphical format as the officially released scenarios. Regarding this I have two questions. First, do you at FFG use some utility specially made to make BoW scenarios? If so, could it be released to the community? It would facilitate the making of scenarios, and I can't think of any commercial or other loss for FFG that could follow from doing so. Second, if the first can't be done, would it be too much to get someone from FFG to convert fanmade scenarios to the official format?
How about holding a scenario design contest? The Warhammer 40.000 RPG crew of FFG have done fan contribution contests from time to time, with great success, publishing the top few entries on the website.