One of the many things that I think might happen in the future, if you do indeed get to such huge figures of data, is movies in games.
The idea is just too hardcore to not come up. Sometime in a not too distant future, there will be a game claiming to have the first full-lenght feature film in-game. It will probably come from one of the major game developers, or at least from a publisher with absurd amounts of money. Because only money is what could keep this from going from a good(?) idea to a fully realized one.
It will not be full resolution, and it will be watchable on TV, maybe even rentable in an in-game video-store.
Wether or not it will be a success is doubtful. Wether or not it will be repeated is also doubtful. But it WILL happen.
Back on topic, how will a 200gb Blu-ray-disc change gaming? Not much. What will it mean for PS3 games? Not much. Why? Because today, gaming is not as defined by technological limitations as it is by resource limitations. Building a game takes time, manpower, money and imagination.