There is just under 30k rooms in WDW (if you exclude non Disney owned). if you went through the same concept as DL, and had blocks every 3 hrs, with 3k(mabye 4K) people per block. You could have about 15k per day in the land.
Since every room requires a minimum 1night stay, that would mean over a 2day period, you could in essence get 30k visitors. I would assume that WDW has a low utilization rate in Sept month, and average stay would at least be 3days. So essentially if you run the numbers you could in fact get all the WDW guests guaranteed a land Rez and still allow for non guests to either use a virtual queue to get in day of (which will be very limited, maybe 10% allocation for non resort guest)