After previously being rumored, Blizzard has confirmed that role locking is indeed coming to Overwatch. It was first rumored for the Overwatch world league, though it will officially be a part of the game itself.. A role queue has been confirmed for regular Overwatch play, therefore instilling the 2-2-2 role lock in the game proper. The change is currently only live on the PTR, but should be coming to all systems in the near future.
For competitive OWL matches role lock would be a 2-2-2 lock, meaning that each team would be restricted to two characters from each role. From the video that leaked earlier, here are the official rules of the role lock:

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