The convention center at Coronado Springs is currently being expanded, I have no idea if the space would be enough to handle a
D23 expo. There are also the two convention centers at the Swan/Dolphin. Part of the issue with having a D23 expo in Orlando is having to ship the models and other stuff from the Disney Archives and Walt Disney Imagineering across country - very expensive. Also, most the people who would honored with a Disney Legands award or who would be tapped for presentations would be on the west coast.
We'll see what happens for 2019 - I would certainly be a happy fan if a D23 expo was scheduled in Orlando.