Just got back from the Reno Air Races and saw a lot of aircraft use full rudder deflection, granted one way, and flip end over end and came out inverted in level flight. I know these aren't airline aircraft but I think a vertical stabilizer is designed to take a lot of stress. Seems like the slipstream alone would make rudder reversals less stressful because the aircraft is trying to straighten it's fuselage with the slip stream automatically.
Remember our A300 came out of the factory with a patched VS so stresses were put on a very small area after the patch. They blamed the FO but as I said before no matter what that previous captain said about his rudder usage I think it was an airframe problem, either the patch or maybe another yaw damper malfunction.
If you take a piece of plastic and put it in a vice it doesn't take too many oscillations to make it break. That is what they did with the delamination, they braced it.