Harmonix has posted about legacy game soundtracks for Rock Band 4, including a very important announcement for Rock Band 3.
Among the different DLC packs, Harmonix is working on getting the Rock Band 3 library exported first. They intend to get it ready in time for the December 4 patch. However, their license to sell Rock Band 3 will be ending this October 30. If you want to get those songs now, including the DLC packs, you will have to buy Rock Band 3 on PlayStation 3 or Xbox 360.
Once you have purchased Rock Band 3 and any of its DLC packs you wanted, you will be able to transfer your songs for a nominal $ 14.99. Only consumers who bought Rock Band 3 will be allowed to export. The good news, if you’re one of those who do buy the game, is that the export will be available indefinitely in the near future.
Were you wondering about exports for other Rock Band games? You can consult this graph for more information.