Githyanki still come up in my mind because they can fit into the framework of the original modules well. And as a DM, I would want the least amount of total re-writing of the module as possible. There would be quite enough work involved in updating stats and creatures within, even without revamping the master races behind the scenes.
They have similar class structures to the Drow with the Warriors, Wizards, Warlocks (f/w), and even monks. And they have enough differences to make things interesting, like Psionics (if you use it), planar abilities, and lack some of the weaknesses of Drow (light sensitivity, Chaotic nature).
Githyanki have societies that are quite advanced. They even have a Lich-Queen (in lieu of Lolth) that is the master manipulator. The end of the series could end up fighting in an astral fortress (instead of Demonweb).
Interesting allies for the players could end up being some of the traditional evil types. Mind-flayers, Duergars, even the Drow might still make appearances to fight against the Githyanki. This could expand the role-playing possibilites by having 'good' characters needing the help of 'evil' creatures to save the day. Moral choices make good role-play.
Anyway, just a few of the ideas I came up with since reading the initial post.