The only "real" brunch is at House of Blues Gospel Brunch over at DTD.
Garden Grove at The Swan has a character breakfast on the weekends that is open until 11:30, but it looks like they only serve breakfast type foods, not brunch type.
Same thing for Chef Micky at Contemporary and 1900 Park Fare at Grand Floridian.
You could schedule a late breakfast at Crystal Palace in MK and possibly get to eat some of the lunch offerings as they switch over, but I'm not sure of that as we've never tried to do it.