According to this article, Sony representatives have confirmed that the DLC content, specifically the missions and maps, will NOT carry over between generations. If you get either of the two expansions for PS3, you will NOT be able to play the new missions or in the new areas on PS4. However, the new equipment from the DLC will still be useable cross-generation, so you can still use that ballin' exotic pulse rifle you got from "The Dark Below" on both your PS3 and PS4. I'm quite disappointed, but I can't say I'm surprised.