More resorts is in the end a zero sum game - all resorts sell out for practical purposes.
If a resort is large enough and desirable enough to pull demand away from - lets say BCV - over the long term, it might free up some BCV availability, but at the cost of its own availability. However, the system has gotten so large, that I don't think it would be noticeable unless it was a huge resort with huge draw.
As the system is in existence for longer, more contracts are sold resale and buyers and owners become savvier. People buy BCV (again, for instance, but it will work with any resort with seven month booking problems) to stay there - and they aren't necessarily enticed by a new resort - not enough to really change seven month demand.
People who bought whatever Disney was selling and have no attachment to their home resort would free up the seven month window - but that isn't the profile of many
DVC members. Especially those that are paying more for a VGF or BCV resale than for an SSR or VAKL resale.