Regular battles will take place on a separate battle screen but the boss fights will take place on the field map, a feature that the team wanted to introduce for all battles, but due to time constraints, could not. Despite Square's claims to a complete overhaul, the battle system will remain the same more or less. The game will be going back to the 3 character party after a brief return of the 4 character party however characters not in your current party will be able to join the battle in some indirect way. The skills and abilities of all the characters will be accessible, whether this will take the form of character swapping or merely joining in for the fight is unknown. Blitzball is a sport, which is said to have an important role in the plot.
Lets hope that they do.
Some character and story details were also disclosed in the article. It would seem that Tidus, the male lead in the game, is a stranger to the land to which I assume the game takes place. He is unfamiliar with the customs and culture. Also players will have a more active role in the story. It is not known if role events like this will play a role in the plot as a whole.