While my original idea was to set in IN SPACE (tm), I realized that fighting evil aliens is a bit more lighthearted than what I had in mind.
Then I got Eberron. To say that it was everything I was looking for and more is an understatement.
So, here's the story idea:
Five years after the Last War, very little has changed. Sure, Boranel's a bit older, Kaius is somehow managing to keep everyone from nuking the world, and Jaela has gotten wise to Krozen's ambitions, although she doesn't know how deep the rot in him runs-which is why he has merely been censured. But tensions are still incredibly high, and the Shadow War has only gotten more vicious. And then Morgrave University and House Tharashk discovered the Ruestli Laboratory.
How Karlan d'Tharashk discovered it in Xen'drik is beyond him, given the amount of more interesting-looking things in the area. The dominant theory is that the Draconic Prophecy led him to the Life-Shaping Ruins, although how it was able to predict that he slipped just so that it tore of the moss covering the runes undamaged enough so that Alain Vellumscribe (sorry if that name is lame, I don't remember the section about Khorvairi names) of Morgrave saw they were not Giant, but a root of Old Common is unclear. In any case, he, extremely interested in this seemingly-anachronistic bit of script, was able to translate it and discover that it was left by a human people called the "Ruestli", which apparently meant "gifted ones" in the closest analogue to their language (ie, Riedran). Under it where directions to a secluded bit of Xen'drik which was strangely uninhabited except by non-hostile aberrant beasts. The expedition, using Karlan's dragonmark, was able to find the hidden entrance to a magnificent underground dungeon, where they discovered that the "aberrant beasts" above it were actually creations of the Ruestli, who had combined an extensive knowledge of biochemistry with reverse-engineered daelkyr flesh-warping techniques to create a science-an art, really-called "life-shaping", the alchemical creation of animals and beasts meant to serve the place that magical technology serves in Khovaire (after learning the bit about the daelkyr, Alain was sorely tempted to destroy the Laboratory, but scholar's curiosity and archeological value overcame justified fear of Xoriat-which, in retrospect, might actually have been a smart move).
After bringing news of this back to Sharn, (minus the "daelkyr" bit), Alain and Karlan sold the blueprints for life-shaping to Cannith and Jorasco, who happily began the process of creating strongholds over the Laboratory to further study the ancient technology. During excavation, a team from Cannith accidentally discovered a hidden camber that looked to be some sort of naval port (despite being, you know, underground). Inside the port, they found the Spirit Knights.
Insectoid suits of giant armor created by life-shaping, these living mecha bond inseparably with their pilots, growing as they do and personalizing themselves to be as unique as the person inside of it. Seeing an extraordinary opportunity for profit, Cannith sold the creature-weapons to all of the Five Nations (including New Cyre, which pretty much eliminated any obstacles to working with them in the future), while keeping the secrets of creating them to itself. Needless to say, this has only inflamed tensions between the Nations (where it not for Kaius having managed to sooth them a little bit before hand, the Last War would have started up again).
Of course, the Knights come with their own strings attached...
The complexity of the life-shaping that created the Knights requires a mind to operate, and with a will comes an agenda. While the Knights truly love their pilots-it's impossible to do otherwise, the method by which they bond is a flawless safeguard-they have a very independent and frankly alien personality that wishes to return to the days of the mysterious empire that created them-namely, by slowly life-shaping their own pilots into Ruestli (in the case of races other than humans, their Knights don't change their race, but they do give them the general appearance and phenotype that the Ruestli had). While this change is cosmetic in nature, given Khovaire's paranoid climate, there is no telling what will happen when the general population finds out. This, combined with the fact that the daelkyr view the "perversion" of flesh-warping with contempt and that the Lord of Blades has found a way to smuggle his troops into the Ruins to study life-shaping for themselves, there are now so many things that could go wrong, and unleash a war that could make the Last War look like a formal duel in comparison.
And this isn't accounting for an undying soldier, the last of the Ruestli, who will do everything and anything to fulfill his last mission-to prevent the conflict that destroyed his home from ever happening again. There's a reason why there isn't any other known archeological evidence that the Ruestli existed.
So, what do you think? Good, bad, just plain stupid?
short version: well done
Personally, I'd bring the big-metal-suits to Khorvaire as a mix of old and new. On one side, I'd have House Cannith trying to parley its now-banned creation forges into the next big thing, and trying to take warforged "technology" in a new direction. On another side, the Lord of Blades could be another source for oversized armor (though these might cross the line between suits and full constructs). On yet another side, the gnomes of Zilargo might see Cannith's developments and reverse-engineer a market competitor through the creative misapplication of elemental binding. On yet another side, some enterprising souls (an adventuring company?) could discover an ancient source for the needed magic/engineering down in Xendrik. Pretty soon you've got an arms race, with everybody experimenting and bidding on the new creations in the name of self-defense, thereby building a castle of tinder on the embers of the Last War. Fun!
The bigger question is: how do you plan to stat out/implement the big suits in terms of game rules? I've speculated, but never fully fleshed out, using a cross between the mount/companion/item rules. That is, most traits still rely on the PC pilot, with some benefits based on the model at hand (mount), some built-in attacks (like alchemy), and maintaining the economy of action and hit points (like with summons).
Let the animu accusations begin!
Yeah, giant elemental-powered suits of armor that require the blood of a dragonmarked creature to operate... :D