Epcot

Date opened: 1982
Size: 200 acres

When it comes to growth, Epcot has been a wild card. Maybe that’s because Disney itself hasn’t seemed entirely sure what the park should be since at least the late-80s. Future World – Disney’s lofty, intelligent, educational “world’s fair” – was meant to showcase the smarts of American industry in monumental ‘80s architectural pavilions featuring lengthy, informative dark rides sponsored by mega-corporations. Each element of that seemed to falter one-by-one until today.

Image: Disney

EXPANSION SINCE OPENING:  With Epcot’s figure-eight orientation and large size (about twice as big as Magic Kingdom), expansion outward has been rare. Rather, new experiences have replaced old throughout Future World, especially. Stories of those continuous replacements fill our Lost Legends library, but essentially every one of Future World's pavilions has lost a beloved or fascinating attraction at one time or another.

One of the most ingenious growths within the park was the construction of the Lost Legend: Soarin’. Accessed from within the Land pavilion, Soarin’ and its impressively large infrastructure were built in a hangar closer to the Imagination pavilion than to the Land - evidence of how existing pavilions can still spread outward from their monumental footprints with auxiliary showbuildings (true of the blue, yellow, and red zones below). 

Image: Google

WHERE TO GROW FROM HERE: Disney is slowly admitting what fans have rallied against for years: that Epcot lost its identity a long time ago to one-off character overlays, brainless thrill rides, and not-so-nostalgic outdated left-overs. The park is famously undergoing a multi-year metamorphosis as we speak. Trouble is, Disney’s solution seems to be… one-off character overlays, brainless thrill rides, and outdated leftovers sold as “nostalgia.” While we don’t yet know how seamlessly it will all come together, we can be sure that Epcot’s growth is largely internal. And we do know of a few areas where dirt is already moving or where projects are certain to take shape.

• Purple (confirmed) - While specifics of Future World aren't exactly clear, overhauls are happening to both the entrance and the inner courtyard, which some suggest will take on a new identity and be called Epcot Center (get it?). 
• Gold (confirmed) - The relatively short-lived Wonders of Life pavilion was somewhat awkwardly wedged between the Energy and Horizons pavilions in 1989 – and true to Epcot form, its interior is currently being gutted to become a pavilion dedicated to Play.
• Blue (confirmed) - Its neighbor – formerly Energy – is becoming a massive dark ride roller coaster featuring the Guardians of the Galaxy. 
• Yellow (confirmed) - A new restaurant is being built attached to the Mission: SPACE pavilion.

As for World Showcase...

Image: Disney

• Red (confirmed) - Though not the first "character invasion" in World Showcase (and inevitably not the last), the duplication of Disneyland Paris' Modern Marvel: Remy’s Ratatouille Adventure will grow Epcot's France pavilion into its neighboring parcel thanks to its very large showbuilding. Speaking of which...
• Orange - World Showcase was built with 9 of its 21 pavilion-sized spaces empty. In the park’s opening year, Equatorial Africa, Israel, and Spain were announced… but they never came. Morocco opened in 1984 on one plot, then Norway was constructed on another in 1988. Thanks to the popularity of the Modern Marvel: Frozen Ever After, Norway expanded into an adjacent plot with the Sommerhaus just a few years ago, and Remy is taking another. That leaves five lots remaining, with Internet rumors suggesting that a Brazil pavilion is in the works for one. But the rest could each host a new country or at least a dark ride for an adjacent one.

As for rumors that both the Land and Seas pavilions are soon to meet the wrecking ball so their properties can be reused for new pavilions? Well… We said Epcot’s a wild card, right?

Disney’s Hollywood Studios

Date opened: 1989
Size: 103 acres

Disney’s Hollywood Studios was – by all accounts – intended to be a half-day park. What else might you expect from a park that offered just two rides on its opening day? Yet those two rides were representative of the two halves of the park: an immersive and historic Hollywood park (featuring the Lost Legend: The Great Movie Ride) and a "working" television and film studio (fittingly anchored by the Declassified Disaster: The Backstage Studio Tour). Though the studio itself quickly closed up shop, Disney awkwardly maintained the illusion of working studio facilities for decades, with the entire back half of the park still dominated by tan showbuildings, studio spaces, and offices.

Image: Disney

EXPANSION SINCE OPENING:  Believe it or not, the original, 1989 version of the park was only what we today call Hollywood Blvd., Grand Ave. and Echo Lake. Meanwhile, the Streets of America, Pixar Place, and Mickey Ave. were all behind-the-scenes until opened up to pedestrians in the ‘90s, and Sunset Blvd. was only built in the years following. In the 2010s, Disney finally ditched the flimsy studio aesthetic as entirely as it could, demolishing and repurposing tan soundstages to make way for Toy Story Land.

Similarly, the Streets of America were toppled and access roads re-routed to make way for Star Wars: Galaxy’s Edge, which will – bar none – be the defining and identifying feature of the park from here on out.

Image: Google

WHERE TO GROW FROM HERE: In its current layout, Hollywood Studios is fairly landlocked by its own access roads and infrastructure on three sides. The good news is that – unlike Disneyland – Disney can reroute and rebuild those roads anywhere it chooses. But for at least the foreseeable future, it won't have to...

• Brown (confirmed) - Obviously, Star Wars: Galaxy's Edge is the expansion looming on the horizon, overtaking much of the land that had been wasted by the Studio Tour and the later Lights, Motors, Action stunt show. Built right up to the edge of the park's property line, Galaxy's Edge successfully "fills in" the park's existing footprint on the south end.
• Purple - Perhaps coincidentally, Hollywood Studios' version of Galaxy's Edge has almost exactly the same expansion pad in the same relative position as Disneyland's version of the land...
• Teal - One of the only outright remnants of the park's earlier "studio" styling is the area around Echo Lake - a mish-mash of intellectual properties, time periods, and "backlot" contradictions that look especially bad compared to the highly detailed Hollywood Blvd. and Galaxy's Edge. Most awkward of all, the land contains Star Tours - now just as redundant as Disneyland's, but also placed in a "studio" style soundstage further betraying the illusion. Of particular interest in the Indiana Jones Epic Stunt Spectacular that's like stepping directly back in time to 1989, still working off the pretense that the 1981 film is being shot live at a Disney Park. Would fans prefer this space become an Indiana Jones land with its own Modern Marvel: Indiana Jones Adventure? Certainly...
• Green -  But long before that becomes necessary, it’s worth mentioning that a huge parcel “studio” space is technically the park’s for the taking. However, in the years since the studio operations moved out, Walt Disney World operations moved in. So while the costuming building may not be making costumes for movies, it’s still making, repairing, cleaning, and storing costumes… just for Cast Members. While relocation of those facilities and offices isn’t impossible or improbable, it’ll be expensive. But it seems almost inevitable that in some point in the future, the path into Toy Story Land will become a crossroads, leading to two "outer loops" in the park's unusual layout.

Of course, Galaxy’s Edge has the potential to change everything. With its two rides added, Hollywood Studios will still have only 9 rides - the fewest of any Disney or Universal park – which may make executives race to add ride capacity.