It sounds funny, but I would be happy with each DLC fixing a chapter in the game lol!
-Chpater 1 needs a biiiiiiiiiiig overhaul
-Chapter 10 needs to give us explorable Cartanica
-Chapter 11 could give us Tenebrae as an actual location rather than a single train station
-Chapter 12 could give us a snowy area with Shiva's statue
I opose 3 of your 4 selections xD
-Chapter 1 is perfect as it is because it starts calm and it's about having fun until shit hits the fan. It's a tutorial to show us the main cast and their dinamics.
-Chapter 2 needs a scene with Cor talking to us about the importance of our objective. Telling us about not going crazy rushing against the empire, how the royal arms and the astrals work and how he will be ocupied forming a resistance that help us in the future.
But i don't feel this chapter needs a new area playable, so i would say to fix this with a patch.
- I think chapter 5 should be the first dlc. In this chapter we learn about Luna's actions. We could change to her as a playable character doing a little event each time we touch one of Ramu's tree's.
We could even play as her in Angelgard against Ramu and end the chapter having a fight against Ravus with Noctis.
I think this is the best moment to build up Luna as a character.
-Through Chapter 6 to 8 there isn't a single cutscene in the game, I think once we reach Caem we should see Noctis hearing a private conversation with Gladio and Iris, with him trying to support her when she breaks down for the death of their family, learning how rough the thing has been for Gladio. Then he ask us to go away to do his Episode.
Again, it's not a playable are, so i see this as a patch.
-I see Chapter 9 as the next candidate to a chapter dlc.
Increasing the action set peace when Noctis has to reach the altar. There we can play the events of the first trailer of XV and reunite with Luna for an action scene against the empire, but without giving the couple time to speak.
Maybe we can fight Caligo in here, seeing how he beat Luna as a child, and making him retreat so Ravus can kill him latter. Also Loqi could be in that fight, so we kill someone of the empire during the game (stupid lemmings killing all themselfs xD).
-Cartanica sounds interesting but i don't know what can be added story wise, and having Ignis blind makes the exploration less fun. If they don't have a reason to explore there, i can't see why to explore an area that looks almost the same compared with the one in the first chapter of the game.
-I also want Tenebrae, copy paste my last post here xD (third dlc).
-I don't know what can be added in the ice part of chapter 12, so i would pass in touching that moment.
-Chapter 13 has to stop being the ugly part of the game, so it should be the last change in the game.
Making the Regalia break far away of the base where the Imperial Star Destroyer is. So we can explore a little peace of Gralea with Noctis and see how all have gone to shit. Also make Noctis contact the Kings of Luuci when he puts the ring for first time.
Once in the Imperial ship where the cristal is, the game should add Verse 2 as an obligatory segment once we find Ravus cadaver. And also shortening some segments with Noct to not make the thing so tidious.
If Episode Ardyn fits anywhere it should be during the revelation of Bahamuth, with Noctis moving through dreams to see how Ardyn was betrayed (and play some segments with him). There we could also learn a little more about Regis actions to set up the journey (Omen and Dawn trailer).