I have spoken with the FAA folks at a few of the gatherings (S n F, AOPA, OSH ) about this very scenario. We discussed the fact that when 2020 rolls around, your display in populated airspaces will be extremely cluttered, and will obscure the underlying data. They totally agree that it very well could cause problems with “eyes inside the cockpit” instead of looking outside. It’s amazing how many planes are flying near you, but before you had ads-b you thought you were the only plane flying that day.
Now you know what ATC sees. But then, they’re not flying the plane at the same time.