Harmonix just revealed that Rock Band 4 is coming for PS4 and Xbox One. So far it seems like a simple port to new generation, but they are trying to import last generation content. When asked if songs and periphals will work with the new game, Harmonix replied that they are working with Sony and Microsoft to gain DLC rights to port to the new consoles. So in that regard all songs will transfer over.
As for the old periphals? Harmonix stated they are “working their asses off” to gain support for them on the new consoles.
This of course comes off the heels of the Guitar Hero announcement which is stated to be “more realistic,” but Harmonix seems to be more blunt when they don’t go that route. Instead they said they “don’t envision Rock Band 5, 6, 7….” and instead stated this will be the one and only Rock Band released for new consoles. Instead they rather work on new experiences.
I think it is rather neat to have all the old content on the new game, especially since is cross generation, but overall it is just a quick way to get the game on new consoles. It’s nothing more than opening it up to an audience again and keep sales trickling in. I still personally prefer them to go the “training” route like Rocksmith has done.