In the real world, there is no immediate consequence for exceeding the "tow rating" by 200lbs. There is no "tow police" waiting in the bushes to shoot out your tires and drag your family off to the gulag the second you go one pound over.
More than likely you won't even be able to tell the difference between 6800 and 7000.
That said, in real world terms, 6800lbs behind a van rated to tow 6800 is going to be a big load. On passenger vehicles, those ratings are definitely on the limit of driver comfort. Performance and handling, while not "unsafe" on a well-maintained vehicle, may try your patience.
Over time with frequent enough use, you may notice accelerated wear and tear in your tow vehicle. If you don't keep up with maintenance, THAT can become an unsafe condition on the road (i.e. running worn/fatigued tires loaded to capacity increases the chance of a failure).
Putting 10-ply tires on half ton trucks since aught-four.