Yes, it's icky.
The Guide to the Astral Plane indicates that githyanki do, at least occasionally, sacrifice people to the Revered Queen. (I'm not talking about the routine soul-eating of high-level Githyanki by the Revered Queen herself here, but ritual sacrifice.) However, as githyanki are neither Aztecs nor Lolth-worshipping drow, I'm wondering exactly how they go about it (I doubt it would be the traditional 'stick the guy on an altar and remove his heart' method).
I'm guessing that the practice is relatively informal -- it probably has an established ritual form, but the when and where are more random, and large-scale sacrifice is probably not common. (For example, if the githyanki ritually sacrificed X number of people every month, the Revered Queen would probably have attained godhood much sooner.)
Are there any other sources referring to this practice?
Here is idea: Githyanki have few alies among other races, but those few that githyanki accept sa equals also grow in power (levels). So I was thinkig that maybe the sacrfice those alies that reach 11 level to lich queen as sign of honor.
For example: human warrior helps githyanki in ilithid hunt and he save some of them in process, they accept him as an comrade in arms and over time that bond grows stronger untill they start accepting him as one of his own. In the mean time fighter have reached 11 level, and gityanki have decided to give him the ultimate honor: audience with their queen.
Truly the gratest honor for non-githyanki.
One-eyed, one-horned, flying, purple people eater says: "Monsters are nature's way for keeping XPs fresh."