Looks like they took some cues from Game Freak.
As promised, you will now be able to download all of your legacy DLC for Rock Band 4, transferring your previous purchases of music to the new game- but this comes with a highly annoying catch, one that almost seems to recall Pokemon levels of frustration with supporting legacy content. You can only download all of your legacy DLC one song at a time. Who came up with something like this?
That’s right, even if you purchased your music in, say, a bundle, you will have to download your music one song at a time. In Harmonix’s defense, this is not their fault- they come clean on their blog, and explain that this is because of restrictions by Sony and Microsoft on the PSN and Xbox Live storefront.
Harmonix provides step-by-step directions on how to transfer the DLC over to PlayStation 4 and Xbox One on its blog. Remember, you can only transfer from PS3 to PS4, and from Xbox 360 to Xbox One- if you’re an Xbox 360 owner who purchased a PS4? Well, you’re going to have some issues.