Only packs that are designated for use with Beatles Rock Band can be used in that game. These are track packs of Beatles songs. It is the same with Green Day Rock Band, only Green Day track packs can be used with that game.
It was released on September 9, 2009. The Beatles: Rock Band is scheduled to be released on 9/9/09.........an obvious reference to the song "Revolution 9" by The Beatles. The game has a website in which you can sign up to receive updates about the upcoming game at http://www.thebeatlesrockband.com/
It has not been suggested by anyone, so it is very unlikely. Luckily, you can purchase additional songs through Beatles Rock Band's in-game store. There is no need for another disk if they can already release more songs in-game.