I bring sad tidings.
After the original githyanki FF entry in in WD12, there are references to it in letters (WD17, 19, 24, 35, 41), the FF poll results in WD18 (in which it came sixth), a WD47 article on demonists in which the spell Summons Army (sic) can manifest a githyanki war party, WD76 (alas, they only feature in a figure painting article by Joe Dever) and WD89, in which they pop up in the name of a games group advertising in the classifieds section.
I checked only as far as 89. I'm fairly confident I didn't miss something as significant as an article but it's possible; my eyes were glazing over at some points.
Had WD commissioned Charles Stross to write a follow-up, I'm sure they would have run it, unless it was scheduled for inclusion then pushed out for some reason, never to find another slot.
I just dunno.