There definitely will be more work on the KH series, as it says on the Frontsite. It doesn't necessarily mean that any work will be done in the near future.

The secret video in KHI didn't imply that there was going to be a KHII. The video just left you confused and "wtf!?" However, since there was a sequel, one can only conclude that there will be work done on the series, based on this clip. Prequel, sequel, or spin-off.

There are alot of things that the video can mean. After all, in KHI, it does mention that there was a legend about the Keyblade wielder: one brought chaos, one brought peace. Infact, if this were a prophecy, it is true. If it was a historical record, this movie may help to explain a game that would highlight the events of KH-0. If this is an alternate dimension, then we will just have to play the new game when it is done.

Both Riku and Sora used a Keyblade at one point, and they did cause an uproar in the worlds they visited. They also fought each other, which caused Goofy and Donald to challenge their loyalties, however misguided by lies of the darkness as they were, and caused Kairi quite a bit of suffering. Riku even worked with the Heartless to capture the 7 princesses. And whenever Sora appeared, something always went wrong. Even Mickey disappeared quite suddenly, and had Disney Castle wondering where he went, leaving his world with a queen that was shocked at his disappearance, and forcing his two main generals to leave the world's defense to their suboordinates (even though Disney Castle was never attacked).

But Riku, Sora, and Mickey also brought peace. They sealed away Kingdom Hearts TWICE, and defeated the known enemy of the worlds, Xehanort Heartless (Ansem DarkSeeker), and Xehanort Nobody (Xemnas). At one point, they caused the worlds to reset, and returned them to a peaceful, yet oblivious state.