For those curious what the D&D Insider article had, here's a short summary...
It mentions the history of the Githyanki and the Githzerai, makes a mention that the Gith were once soldiers of the Illithids. Goes on to mention Gith's uprising and the split with Zerthimon. The pact involving Tiamat with some of Dispater's manipulation, is described. They actually tell what happened to Gith herself, and mention some of what happened in Paizo's Incursion with how Zetch'r'r came to power and spoil what happens in Scale of War, saying how the spirit of Gith escaped and is back.
The city Tu'narath is described in some detail, like how it was somewhere they fled when the Githyanki couldn't find allies and a safe haven. With speculation on who the Dead God the city is built on might be. And a bunch of the stuff that was written on the Githyanki in Guide to the Astral Plane is presented here again.
What's new beyond the Scales of War stuff, is some of the stuff about the Dead God and Primordials, and the theory introduced back in the Psion article on how psionics might have been the World's reaction to the Far Realm's intrusion into reality.