Along with this rumored feature, the site has posted a list of upcoming DLC, including 10 tracks from Queen and three from The Raconteurs due in October. Three songs from The White Stripes are listed for November release. Undisclosed material from Attack! Attack! and The Duke Spirit appears as undated Rock Band Network content.
When contacted for comment, Harmonix told Joystiq, "While we don't comment on rumors or speculation with regards to our upcoming downloadable content, we can promise that the Rock Band platform is poised to remain the unchallenged best value and source of music for rhythm games."
This supposed "leak" is very conveniently timed, given that Guitar Hero 5 releases tomorrow. Doncha' think?