Considering Aranea's DLC is being sold as an opportunity to see things from Niflheim's perspective I'm gonna assume for now that, that is our Niflheim episode. Also considering Noctis is getting an Episode and they'll likely be constructing new assets for it while also changing things up to make the Episode stand on its own so I wouldn't rule out getting to explore Insomnia in a less destroyed state just yet. Who knows, maybe Noctis' extra mode in his episode is an Insomnia tour or something as an optional thing similar to how Gladio had a score attack mode, Prompto had racing, and Ignis had a straight up alternate story path. It's entirely possible they'll include some more cool extra bits of gameplay to experience once you get done with the main content. Considering that it's Episode Ignis' director helming all of these episodes I'm expecting the optional stuff to be just as meaningful as Ignis' "Extra Verse."
This. Guys, I think we really need to stop being salty about what is coming out. It's done at this point and they aren't going to change the plan. This is what we are going to get. ALL 4 DLC's have massive potential to address all of those issues. We can get more Regis, Insomnia, Niflheim, and more through these 4 DLC.
No matter what happens, everyone won't be satisfied. It's just the curse this game has had since it was made. It's just too large for one and no matter what DLC or section of story they pick it will never get everything touched upon.
But...
1. Episode Ardyn has the opportunity to cover several different events in FFXV (Ifrits revival, Shiva's death, 2000 years ago when he was betrayed by his Brother, the Crystal and Bahamut). Whichever are covered or if all are covered it can entirely solve the Eos lore problem the game has (which they said they intended to fix with this DLC). The episode still has the ability to add new areas in Niflheim or places we havent seen yet. It's also the DLC most people wanted.
2. If Luna's episode is before her death, they can address the things she did between KG and Altissia, maybe even expand Accordo a bit more. If not, Tenebrae is its other top contender but I am unsure what she would accomplish here. If it's after it can wholly address the afterlife concept FFXV has. Overall it has the chance to elevate her character in ways we haven't seen.
3. Aranea's DLC is giving us the opportunity to expand upon Niflheim once more. Whether or not that is just Gralea or Tenebrae, remains to be seen, but also could be several areas. Self explanatory, I really think this one and Ardyn's will be very satisfying in the least.
4. Lastly Episode Noctis could give him some new OP abilities and ways to play. AGAIN, we do not know how the alternate finale will affect the main game. It could very well be like chrono trigger, or Nier, where the game has a definitive ending but other endings could shed a lot of light in the lore or canon of the game itself.
After much time thinking I definitely don't think alternative endings are a waste anymore, depending on how you tell them and how integrative or important they are to the main story. This ending could very well be canon to the main game depending on how they connect it, even if it's not the original ending.
Also, everything above was mostly from the June poll, save for Noctis's stuff unless it has to do with the Noctis's disappearance selection.
Just wait, be patient for more info. These could turn out to be the best content the game will have and we could all be shitting on it now for no reason. Just because something is alternative doesn't mean we won't get a slew of new gameplay mechanics and areas to explore.
Just think on the bright side