20-Year Prospect
Unless someone figures out a way to make the transporters on Star Trek a real thing in the next twenty years, air travel will continue to be the fastest way for folks to get from Point A to Punkt B, el punto C, or Punt Z...and that means that air traffic controllers will definitely still be with us two decades from now.
There are obstacles you'll need to overcome if you want this gig, however. While the Federal Aviation Administration (FAA) isn't likely to cut back on the number of air traffic controllers it currently employs, budget weirdness (thanks, Congress) will probably stop the FAA from hiring newbie controllers eventually.
Furthermore, the Feds are putting a billion dollars a year into a new air traffic control system called "NextGen," which will make air traffic controllers more efficient than they already are. That means—you guessed it—there will be fierce competition for the few controller jobs that remain available.
While air traffic controllers will always be around to ensure that the rest of us get to fly the friendly skies, the job market for this career could shrink once new systems are in place. That's not likely to happen too soon...but be aware of it on the horizon.