DHS is on track to get a single mediocre Family Coaster and Epcot should be getting its' Guardians Attraction. While the two Star Wars Attractions and Flight of Passage should be great and more intense, impressive coasters aren't really in abundance. Guardians should be the first notable add on since Everest.
Magic Kingdom has only 4 coasters, and 3 of them are more on the mild side.
There's certainly room for a new addition, whether Tron or something else.
More critical in my eyes is getting Magic Kingdom something boundary pushing in terms of technology and scope. A true 21st Century Attraction. The other three Walt Disney World Parks will all have cutting edge super E Tickets within a couple years, Magic Kingdom deserves to join their (and IOA's) ranks. Every other Castle Park except Paris has one or will have one soon. Tomorrowland presents an interesting opening to use technology in compelling ways. Magic Kingdom feels old, and needs a shot in the arm.
Tron would fit the bill. That attraction is awesome and would instantly become one of the top rides in Orlando. It's the type of attraction teens and young adults would rave about. So would something along the lines of Battle Escape or Battle for the Sunken Treasure.
They could also modernize Space Mountain
Though I'll once again add my disapproaval for removing the Speedway before other expansion pads have been utilized. Seems like another way to save Disney money and mitigate capacity improvements. Let's add capacity, not trade it.
Magic Kingdom is perhaps Disney's most important Brand, powering billions in revenue and profit. It's time they showered it with the attention it deserves.
Paris' Pirates is so good it is truly a super-headliner TBH, and the park is so pretty that it makes up for a second one.
Space Mountain: Mission 2 is what The Magic Kingdom misses, an epic thrilling coaster.
There's not a single very thrilling ride in the entire Magic Kingdom.
It's long overdue. The Magic Kingsom needs a dark ride, a very thrilling coaster, and a super-headliner like Indy or Forbidden Journey.
Since all 3 are not going to happen anytime soon (mind you, there has not been an epic scale attraction since Splash Mountain, and then they closed 20k Leagues Under the Sea so we are in a defecit for over 20 years for the most popular park in the world!!!!!!!!!!) I really hope at least one of those 3 happens. Any would be welcome. A super high quality dark ride, a super headliner minor thrill ride, or a very thrilling coaster. Just look at the waits for the thrill rides at the park, capacity is an issue for the demand, but then we're back at the issue of not everyone can enjoy them, so MK truly needs a not that thrilling big ride first, but please don't complain with whatever they chose because MK needs something so darn badly.
It's absurd the amount of time to have to wait for rides at WDW. These rides are good but are not above and beyond attractions... SDMT, Space Mountain, Soarin', Test Track, Rock n' Rollercoaster etc. Meanwhile just down the street while their second tier attractions suffer from the screen problem Universal has so many mind blowing attractions. From Spider-Man to Forbidden Journey. It's a shame that the Magic Kingdom has not gotten a single one since before IOA opened. Pretty sad isn't it? Even though it has over twice of both Universal's parks' attendance combined.
The only reason it's bearable is because we mainly enjoy the park instead of just the rides, and thankfully we book fast passes in advance, but it's still quite crazy when you think about it.
Guests would enter a winding pathway between pirates and jungle cruise into what appears to be a volcano guarded by an ancient evil 
