In Chapter 62 of Genshiken, nearly all of the girls cosplay, and in my review I talked about how appropriate it was that Ogiue would cosplay as Azusa from K-On! Upon reading the more recent chapters of the K-On! manga though, it hit me that Ogiue-as-Azusa is an even better fit than I first thought.
Ogiue and Azusa are somewhat similar in personality in that they both act stubborn but are in reality actually pretty easy to persuade, but they also have similar positions within their respective clubs and within their stories. Ogiue and Azusa are both younger members who join the current incarnations of their respective clubs after they have been well-established. They then both end up taking over their clubs after the other members graduate. In either case, this seemed like a good opportunity to stop the series. Genshiken was originally complete at volume 9, and for K-On!, rarely does a moe slice-of-life show about high school girls end up going past graduation (see Azumanga Daioh). But both series continue on, showing Ogiue and Azusa in their roles as leaders while also giving face time for the older former members.
There are also a bunch of smaller things, like how both clubs are notoriously bad at getting new recruits. With how Kio Shimoku ends each chapter with some line from an anime or manga title, I am 99% confident that he picked Azusa as Ogiue’s cosplay for these reasons.