In another topic, I've discussed the party my players made for their first Eberron adventure. I'm still brainstorming on a couple of points, and I'd like to get some ideas. I'm new to Eberron, so the more expert ones might have some good inputs.
A dragon from the Vast who is part of the Chamber was murdered. I imagined he was part-time in the Vast, and part-time in Khorvaire doing what members of the Chamber do : manipulating events to favor some outcomes of the Prophecy. I imagined him a "young" gold dragon, not really aggressive. He probably was more a contemplative kind of dragon. He might have been slayed by another dragon from the Chamber, which in the end will show to the players that dragons don't agree on everything and have their own agenda. I'm still trying to figure out the reason for this murder. Something found recently in the draconic prophecy ? Maybe another dragon brought him some new cryptic parts of the Prophecy, and once it has been translated and explained, maybe this dragon wanted to be the only one to know about it. But about what ?
I'll see what comes up from here. If it allows me to find some interesting ideas, I might give you some other elements for which I'm brainstorming.
Thanks for your great ideas ! 
One of the coolest things about the Last War was the constant shifting of alliances to meet one's own end. There's always improbable team ups to be had that share a common goal.
Why not change the member of the Chamber to a Rakshasa in disguise? The Lords of Dust are everywhere, and may not make things as easily understood that another individual/organization is involved. Perhaps the Chamber is after an artifact that another nation or organization like the Aurum is after????
Thanks for your inputs. I'll definitly have a look at Zenobaal. But my PCs will start lvl 5, so this will not be the first bad guy they'll meet. :D
Talking about changing the chamber dragon into an agent of the Lords of Dust, it gave me an idea ! Instead of a Lord of Dust agent, he could be a Chamber Dragon who has strong dreams. I mean very inspiring dreams... And the Dreaming Dark could probably be behind this. I choose the DD, because one of my player choosed to play a Kalashtar, and I think this would be a great motivation to get him involved.
Here is the outline I have right now (consider visiting the previous link to fully understand this discussion). A (green ?) dragon is an active member of the Chamber. He is located in Aundair, close to Arcanix, and manipulates a small group of Silver Flame extremists who are members of the Arcanix. Through them, he get many information from the Arcanix. My PC feral who manifested an aberrant dragonmark during a lecture in Arcanix was targeted by one of those zealots, but he escaped. Maybe only from here, the dreaming dark starts to manipulate the green dragon (I'm still missing their motivation here though). They could provide him with a false part of the Prophecy to make him try to kill the Feral, or maybe he unraveled a real part of the Prophecy mentioning (in a very cryptic way of course) the feral with the aberrant dragonmark, and killing him would further his destiny (or so he thinks). In order to understand the part of the Prophecy he discoverd, he had to seek the assistance of a more enlighted dragon - a gold dragon from the Vast (also a Chamber member) who is at the head of a small dragonborn tribe (one of my PC originates from this tribe).
During his stay in the Vast, the green dragon turns the dragonborn sorceress from the gold dragon's tribe to his side. If she uses on the gold dragon a powerful poison he provides her, he will grant her with mighty powers. He wants to slay the gold dragon because of his knowledge of the Prophecy he just translated. But he doesn't want to do this himself, fearing the Eyes of Chronepsis.
The sorceress poisoned succesfully the gold dragon. She betrayed him once more when the gold dragon, weakened by the poison, sent part of his tribe to Khorvaire, trying to find the green dragon and get an antidote. She warned the green dragon who organized an ambush. Only the sorceress and my dragonborn PC survived this amush.
One of my PC is a chageling artificer. He's an Aundairian spy posing as a Valenar elf. All of his previous identities have been compromised by another agent known as The Shadow. Now I think I will make the Shadow another dragon. He's either from the Chamber of from the Eyes of Chronepsis. He's using the changeling to investigate the death of the gold dragon, and actually the green dragon who apparently went rogue (actually manipulated by the Dreaming Dark). I like the idea a lot, because the Shadow seems to be an opponent to the changeling, while he is actually an ally (or patron of some sort). Sure he is using the changeling. But he is from a lesser race... This could provide me with an excellent climax, where the characters face the dragonborn sorceress and the green dragon. In this context, their situation is hopeless. But the Shadow could then appear. I would imagine the green dragon escaping, the Shadow trying to stop him. The PCs would face the dragonbron sorceress themselves. Afterwards, the Shadow could still use the PC to try to locate the green dragon who escaped succesfully.
Any other ideas, thoughts, suggestions ? I'm still looking for the reason why the Dreaming Dark would be involved. I understood they try to keep things "unsecure" to prevent their age from passing. Is the Prophecy about the Feral real ? Or is it a lie coming from the Dreaming Dark ?