We have approx 163 cabins still available (I used Chrome Dev Tools to spit out the JSON data for cabin availability for our sailing... these do not take into account Guarantee cabins that eat into this number) for our Disney Dream sailing in late September. Out of 1,250 cabins, it doesn't seem out of line for 13% of them to still be available a couple months before sailing.
Obviously, Disney would prefer each sailing be sold out, but I'm even more interested in knowing what % sold they think they need to hit for their Concierge customers to feel justified in spending significantly more. Concierge customers might feel it's a waste on an empty ship; the benefits increase as the ship becomes more crowded. So they do run a pretty dangerous game of losing out on high-margin Concierge sales if they don't keep demand consistent. That's just speculation on my part, but I don't think every Concierge customer is "ride or die" with Concierge.