Update: An EA Sports graphic has been released, showing which parts of Ultimate Team are accessible at any time in each game, and which are one time transfers only.
Essentially, all elements of Ultimate Team besides FIFA Points are transferable between generations. FIFA Points can be moved from current to next-gen in a one-time only transfer.
Original story:EA has announced that FIFA 14: Ultimate Team's full-roster, in-game items and in-game currency will be accessible between both the Xbox 360 and Xbox One and between PS3 and PS4.
These changes will be reflected in both consoles allowing individuals to compete with their squads on whichever machine they choose throughout the season. In short, if you want to start on the current-generation of console before moving onto the next, all your progress will come with you.
Auction houses will also share a common market between the respective platforms, meaning Xbox and PlayStation owners will have their own place to buy and sell players without having to worry about the machine they're using.
FIFA 14 is due to be released on September 27.
Source: Press release