As a computer progammer, I really like the Draconic Prophecy. I imagine it as very elegantly written code, incredibly long and incredibly powerful. So I've got a plot device that I introduced to the players in the form of an artifact I'm calling The Book of Names, the Many-Eyed Shard or Seeking Crystal. Basically it....actually I don't know quite what it does.
I used the age-old method of introducing a plot device that I didn't have to write up, and now I need to actually give it some attributes.
I want to make it something that a surveillance or information-gathering organization would have use for, and originally the idea was that it was sort of like a Prophetic search engine. You indicate what part of the Prophecy you want, and it returns information on that particular part, including passages that reference that particular input.
Its name came from the fact that most of the users associated with it in the myths used it to locate individuals, but theoretically it could locate things and places as well.
I'm having trouble deciding if I like this idea, so if anyone could put forth an alternate use or some other sort of condition attached to its use that would be very appreciative.
As a caveat: its current incarnation makes it interesting in the subplot I've developed for two of the characters: a pair of players are playing drow, one is the father of the other, and they've decided to manifest different marks.
I was originally against this, but worked up a story about a group within the Chamber who used House Vadalis, Sivis and Cannith to experiment on artificially manifesting dragonmarks. The drow pair are the side-effect of one of these experiments.
While that's a fun subplot on its own, the real fun comes from the fact that the dragonmarks act like pointers in the C programming language. Specifically, when the Prophecy "checks" to see if certain mark-carriers are present during an event, the fake-marked will trigger the event the Prophecy was calling.
So how does that sound?
What if dragonmarks appeared in the past - during the age of giants on the skins of the Drow.
The Giants couldn't stop this manifestations of dragonmarks among the drow population from happening.
On one hand they wanted to do research/experiment on those drow slaves that got the marks, but they also feared the marks will trigger a slave rebellion.
so they inserted a kind of a "Conceal Dragon mark" ritual built in into the Drow lineage, they will still manifest the dragonmarks but it will not be visible and the drow will not be aware of it.
The "Book of Names"/"Seeking Crystal" was then created by the Giants as a way to both locate those drow that had the marks and to counter the "Conceal Dragon mark" so that the drow's dragonmarks can be researched in the safety of the lab.
Not to sound dismissive of your idea, because I appreciate the assistance, but I feel that making those changes only further distances my incarnation of Eberron from the accepted setting. Having the drow manifest dragonmarks on Xen'drik goes completely against both the assumption that only some races get dragonmarks and the fact that they only get them while on Khorvaire. My drow players didn't manifest their marks in Xen'drik, but in Khorvaire.
Also, I think your explanation for the Book of Names limits its power to a degree that makes it kind of useless. If it only reveals the holders of dragonmarks, whether they're concealing it or not, isn't the kind of world-shaking power that I was hoping for.
The idea was that it was a creation by the dragons to help read the Prophecy, and anticipate what needed to be where before certain events would occur. I can almost imagine several dragons on Argonessen carrying around Seeking Crystals like we do PDAs, and opening up a passage from the Prophecy.
Thanks for the ideas, but I'm sorry to say they're not quite what I'm looking for.
Perhaps the Book of Names returns the parts of the prophecy related to a properly asked question (ritual needed to format the question), with precedence for the answers based on the settings of 3 different observatories - 1 in Darguun, 1 in Xen'drik, and 1 in Argonessen. However, the Book is very thorough. It will immediately return an answer. 5 minutes later, another answer, 10 minutes another, 20 minutes later another. Over time, the interconnections will become apparent, and contradictions may appear. Depending on who asks, the answers may be pictures, dreams, phrases, etc. Until the ritual is learned, most of the answers mean something like "to contact the home office for help, travel to location X"
The characters can discover they need to learn the ritual to "properly" form a question, campaign arc.
Along the way, they learn about the Darguun observatory, maybe because they travel there to learn the ritual.
Then Xen'drik, Paragon. And Argonessen for Epic.
As they get better and better with the Book, more and more NPCs and organizations will take note.
Some more ideas then:
How about the "the Many-Eyed Shard" allows the user the see trough the eyes of dragonmarked people.
For example it could be used to see what the heads of each house is doing at any given time.
It could be even store all this information into dragonshards and notify its holder (using a telepatic or visual flashback/flash-forward) about a person that he just passed by on the street, or an event which is going to happen based on the collected stored data (somewhat like the t.v series Chuck).
If we're going with a computer-programming theme why not go the whole hog? Perhaps the Dragonmarks as we see them are pure compiled history, they represent the physical manifestation to our limited consciousness of possible polymorphic future outcomes. It also explains why it takes so long for anybody to actually decode this information, it's not in a form that would be considered language based as we generally know it (the dragonmarks are byte code and converting them into a source-code language that we know such as Elven or Common isn't easy).
What the Timeless Array (my name for your MacGuffin) does it something akin to a reverse-Parser, it's able to read the raw Prophecy and generate information in a higher-level language. In plain english, it reveals to someone what they are looking for by reading the local underlying code of the Prophecy that's written in everything. From the way the wind blows the leaves to the arrangement of puddles on a road and their general shape.
Your two drow are acting as something of a catalyst. Because they represent roaming points of prophecy, or as you mentioned earlier, they are pointers (to borrow another computing term). They help the Timeless Array more readily read localised Prophecy data.
Heck this is starting to smell like p-math :P .
If we must resort to computer science terms 
:
Then if the prophecy is a fully compiled code (unreadable as it written in Progenitor (machine) code), then the MacGuffin allows to set breakpoints on dragonmarked individuals (which are areas of the compiled code where debug information have been added), once at this break point you can watch the heap/stack variables which will help you figure out what functions (historical events) are going to be called next.
What if someone has been scrying (pressed rec and forgot all about it) with this device for many years now (a lord of dust / a chamber agent / undying court) and collected a library of dragonshards which recorded every dark secret of the dragonmarked members: heirs ordering assassinations or even all the way back to the creation of Erandis d'Vol as a lich and her actions since.
and maybe one of this storage shards have been discovered and everyone are rushing to find this actual device/library.
You see I like to think of artifacts as interesting plot devises that string the story along for a little while directly, and then they launch the story forward with their leaving and eventually the PC's are sucked into the consequenses of having or using the item in the later game.
Now as far as I remember, the Dragons currently run around finding the markings of the prophecy on everything in the world, sometimes etched on the sides of mountians or found in the veins of a specific type of flower, and recently on the flesh of the 'lesser races' of the world. They are compiling the data so that they can read the finished product, each individual mark acting like a small piece of data that needs to be added to the database before it can be understood. All the marks and all the prophecy may be one large program running to its conclusion, but the people of Eberron can never see all the code at once - only small parts of it.
So as far as an artifact that reads the Draconic Prophecy goes I would give it the following powers:
- The owner can use a new ritual once per day from the item called "Read Dragonmark" that once cast inputs the marks meaning into the item for later use. Or perhaps implants it directly into the casters head and then places the corrisponding mark on the characters body somewhere removing it from the area it had occupied previously and draining it of power.
- The ability to point the holder in the direction of the prophecy mark that will allow them to answer the question they have most recently given - if the object is a book it draws a map for them within its ever shifting pages, or if it is a shard of crystal it glows and floats in the direction of the mark as if a compass.
- Also make the book something that can be at least slightly useful in combat. I know this is not really needed, but PC's tend to like to have really powerful weapons, and it will make it more memorable in the long run. I would make it usable as a wizards tome - but then again I dont really know your group composition so that wouldnt work if you dont have a wizard...
Anyway thats my two cents...