Actually, this isn't quite right.
I think you might be referencing this comment from Reddit:
https://www.reddit.com/r/Rockband/c...4_on_pc_gasp_crowdfunding_campaign_is/d0jjch8
Criss was commenting in general that we want to carry entitlements forward, but in this case it's more complicated since the Sony RBN songs are ONLY available on PS4, not Xbone (because the 360 RBN songs were automatically submitted by XNA, but the PS3 RBN ports were submitted by Harmonix, and therefore part of the regular DLC entitlement to PS4).
So in this case we can't commit to doing what you describe above. We MIGHT be able to, but we might also require songs that are re-submitted and then ported to the new consoles to be a unique version (e.g. "Song Name - RB4 Version") with a separate entitlement.