Oh boy, this is a big one.
Vlaakith, the lich-queen of the githyanki, has been killed (or has she?)! The whole epic-level Incursion plotline could make the Astral plane a really interesting place.
Not only is the three-way war between the githzerai, the illithids and the 'yanki going to be affected (one of the big conflicts of the planes), but suddenly we might start seeing some really powerful githyanki subgroups popping up and seizing control.
No doubt there are plenty of githyanki who chafed under her rule, and this is their opportunity to do something about it. And what about the githzerai? Will they try to use this opportunity to destroy them, or bring them into the fold (an interesting dilemma for the zerths). And the illithids?
But is Vlaakith *really* dead? Liches are notoriously difficult to get rid of, permanently. Obviously, her control has been diminished, at least for a while, but is this an opportunity for her as well? What of Gith and the pact with the red dragons? What what what!?
One thing to note is I feel the most obvious contender for "Top Dog" status in the Astral isn't the githzerai or the illithids at all.
The *Psurlon* are the ones I'd see as the biggest immedate benifeciary of a weakening in the githyanki defenses. They've got hte population to do somethign to the githyanki, and the motivation since they live almost entirely in the astral as well.