(Note: I rarely make threads of my own, criticism is welcome)
So, what do we know?
We know that Kairozdormu will help Garrosh get to Draenor of the past, creating an alternate timeline.
Now, we know of two places in the universe of Warcraft were time is somewhat unstable and shifty, the first being the Caverns of Time, the second one being Karazhan. Time and space seem to flow in unnatural ways in there. This, combined with the fact that Karazhan has recieved some attention now with a cleanup, has lead me to the following theory.
Everything from here on out is pure speculation.
Kairozdormu, has at some point in the past, or is about to, venture to Karazhan. His intentions? Might just be curiosity. He may have heard about the strange ways in which time seems to work in there, and thus goes there to learn more.
In there, he discovers a hidden path, that takes him to the rumored lower Karazhan, an upside-down version of the tower, extending down below the basement. He makes is way to the "top" of this inverted tower, and as he gazes out through a window, he sees an alien world. Draenor.
The path to the inverted Karazhan turns out to be a portal through space and time. An old experiment by Medivh, perhaps. Maybe he created this portal in an attempt to reach a world were he could sit, silently, by himself. It's possible that Medivh had no intentions of ending up on Draenor.
Kairozdormu studies the portal, and learns some of it's mysterious working.
Fast forward, he helps Garrosh flee. He might have been able to open another, small portal to Draenor. Or, what I find to be more likely, he takes Garrosh with him to Karazhan and leads him through the already existing portal. We, the players, chase after them. The portal is probably small, and unstable, we are hesitant to go through. It is decided that a select few, brave souls will travel through the portal. Amongst those select few is, of course, the player.
We find ourselves on Draenor, and the portal seems to remain stable. For now, this small portal remain our only gateway to Draenor, but we soon learn about Garrosh's plans to open a new portal on this alternate Draenor, and connect it to our very own portal in the Blasted Lands. What remains of the Horde and Alliance armies gather in the Blasted Lands, prepared should Garrosh succeed, while we work to sabotage his work through the small portal in Karazhan.
This is how I see the expansion starting off. Most of it could probably go into the pre-patch before WoD hits.
This could also explain, finally, how Gorehowl, the legendary weapon of Grom Hellscream, ended up in Karazhan. This has never been explained and is by all means considered a "lore-less" placement of the weapon. Maybe when we go to Draenor we find that the alternate version of Grom is not wielding his iconic weapon. It could have gone missing. One of our first quests in an attempt to get on the good side with him, which is probably what we want, could be to retrieve Gorehowl for him.
So, thoughts? Too far fetched?
EDIT: I see now there is quite a big thread going on this subject already, perhaps I should've posted this there instead of making a new thread.