Swan/Dolphin has 329,000 sq ft of convention space and a 55,000 sq ft ballroom, but the Boardwalk, and Yacht & Beach club convention centers are close by too.
This topic comes up every two years during D23 Expo time. Folks who have never been to Anaheim and/or D23 Expo understandably wonder why Disney doesn't try a D23 Expo in Orlando instead of only doing them in Anaheim. The short answer is; there's just not nearly enough room on WDW property for D23 Expo. The longer answer is...
Add the 330,000 sq ft at Swan/Dolphin to the 460,000 sq ft at the five other WDW hotels and you've got 790,000 sq ft total to work with, versus the 1.6 Million sq ft they are working with all under one roof at the Anaheim Convention Center. But the 790,000 sq ft at WDW is split up over seven hotels, much of that space is smaller conference rooms and reception lobbies, and the biggest single space you've got is the 65,000 sq ft Coronado Ballroom.
Then look at how D23 Expo uses the space they had at the Anaheim Convention Center (ACC). D23 uses some very large venues within that center. The most important and unique venue at the ACC is the Anaheim Arena, which they use in a 8,000 seat theater format for opening ceremonies, major keynote addresses, and executive presentations each day of the Expo.
D23 Expo Arena - Keynote Addresses & Executive Presentations
The Coronado Ballroom can be turned into a simiilar theater, but it wouldn't be tiered and the maximum number of seats is 6,600. So you could turn the Coronado Ballroom into its single level theater format and max it out a few times per day, but that takes it off the table for any other Expo uses.
Then there are the smaller Expo theaters; Stage 23 on the 3rd floor and Stage 28 on the second floor of the ACC. Stage 23 uses the 38,000 sq ft format for that ballroom with seating for 3,800, and 6,000 sq ft for queue. Stage 28 uses the 10,000 sq ft format for that ballroom with seating for 800 and 4,000 sq ft for queue. The equivalent at WDW is the 55,000 sq ft split into two theaters in the Northern Hemisphere and Southern Hemisphere ballrooms at the Swan. So now you've got a keynote theater and two smaller theaters set up for 3D and/or HD film presentations with high quality audio systems; spread between the Coronado Springs and Swan.
Then you've got the sprawling exhibit floor itself, which at D23 Expo uses exhibit halls A,B, C and most of D at the ACC. Those ACC exhibit halls have a combined space of 675,000 sq ft. The WDI Pavilion in Hall C uses 150,000 sq ft alone, but other major offerings above 100,000 sq ft are the Dream Store, Collectors Forum, Disney Interactive, and Disney Consumer Products. All of the remaining exhibit space in WDW could be used thusly;
150,000 sq ft Dream Store downsized to 86,000 sq ft for Coronado Springs Exhibit Hall, using 21,000 sq ft Fiesta Ballroom for required queue
150,000 sq ft Imagineering Pavilion downsized to 46,000 sq ft Fantasia Ballroom at Contemporary
25,000 sq ft Mickey's Of Glendale downsized to 8,000 sq ft Nutcracker Ballroom at Contemporary
100,000 sq ft Disney Consumer Products downsized to 18,000 sq ft Grand Floridian Ballroom at DGFH
100,000 sq ft Collectors Forum downsized to 38,000 sq ft Grand Harbor Ballroom at Yacht Club
35,000 sq ft Disney Interactive downsized to 11,000 sq ft Promenade Ballroom at Boardwalk
And now we've used every large ballroom or exhibit hall on WDW property. There's nothing left. But there's a lot of stuff that didn't make the cut; ABC Television, the 50,000 sq ft
Treasures Of The Disney Archives exhibit, Disney Channel, Disney Citizenship, and all the smaller corporate exhibits from Disney Weddings, DVC, Disney Cruise Line, etc., etc., etc. You could use Epcot's 60,000 sq ft World Showplace hall for some of that stuff, but still you'd need to cut things down drastically or ask some groups to not host an exhibit.
But just to get the major players and largest exhibits onto WDW property, we've had to cut and hack everything to pieces, downsize everything by big percentages, and spread it across every ballroom and hall on the property. The logistics of getting everyone around to the various hotels and venues and events would be nightmarish, and once you got to each thing it would be in a much smaller format than the first four Expos in Anaheim from 2009 to 2015.
Which is why it's said every two years that D23 Expo in its current large format will never be able to be held on WDW property.
The only option would be to host D23 Expo at the massive Orange County Convention Center on I-Drive. That center is even bigger than Anaheim's center at 2.1 Million square feet, and could easily take on D23 Expo without breathing hard. The tough part there is now you've got this major Disney event not on Disney property, and it's 9 miles away on I-Drive and I doubt Disney would want to lose that important company vibe to I-Drive. Much less have to deal with the transportation logistics of moving 50,000 people to and from WDW property and I-Drive every day for the Expo.