I think the time to start that is now. Right now, Disney has the most DVC properties available (at WDW alone) that it has ever had. Saratoga Springs, Bay Lake Tower at the Contemporary, and the Animal Kingdom Villas all have large unsold inventories. Additionally, the resale market has the largest inventory that it has ever had, and prices both direct from Disney and via the resale market continue to drop to their lowest amounts in several years. It's quite easy to blame these numbers on the economy (and there is no denying that the economy is causing some of the decline), but why not take a different approach?
Rather than shrugging off the poor numbers as a result of the economy, why not adopt the DL tactic of creating seasonal offerings and plussing attractions? Market these changes as something WDW does to specifically appeal to those DVC members who want to visit yearly or even several times per year. (For those unfamiliar with DVC's current marketing strategy, it is solely aimed at looking at all of the places besides WDW that you can stay. However, these "outside offerings" (besides Vero Beach & Hilton Head Island) offer terrible value for your money, and most DVC members join to stay at WDW). I think at some point, WDW will have to adopt similar practices out of necessity, or they will begin to face an outflux of members (those who bought-in in the early 1990s) who have grown tired of WDW's offerings. However, when will that point occur? I don't think we've seen such an outflux yet, nor have WDW's AP numbers reached a high enough percentage of total guests that management believes they must adopt such a strategy out of necessity, but surely it isn't far away.
Whether you love or hate all of the DVC properties being built, I think we should all appreciate DVC for what it offers to WDW that would never otherwise exist: demand for those "little things" that DL does to attract repeat visitors. Hopefully WDW adopts similar strategies soon!