The dream segments were all the Luna cutscenes; we were probably going to get an info dump in the Forest of Memories, seeing the memories of Regis and Luna as well as a memory hidden away in his mind; Regis cutscenes were most likely going to be insight into Kingsglaive or the events of EP: Ardyn, and Luna cutscenes were all of her scenes that were flashbacks in the game. Noctis was going to remember his time with Luna, his time with Regis which he does in the main game but they're brief flashes showing Ardyn's presence in their lives before he wakes up (presumably these three flashbacks were added because they couldn't add the Forest of Memories). The Forest of Memories, a place he accesses only in his dreams, seems to be the same forest from Platinum Demo wherein he discovered Carbuncle. Umbra having the Astral Memory, allowing Noctis to visit his memories seems like the compromise they made. Noct may have also seen the Dawn footage, as he was getting Regis and Luna's memories; he'd have seen how Niflheim treated her after they invaded, he'd have seen his father's reaction to him being chosen. With this new perspective, he wakes up determined and a changed man with a broader understanding of what he must do. The DLC itself seemed like it was simply going to explain the phantom wedding scene, as in death they are united, a place we were to explore with Luna in her DLC.