In my mind, Gossypedía could be a compilation of virtual books, as such, the option of subject/topic wise is preferable. This is indeed the most common option we find with wikis.
If one has a subject in mind, he/she can submit it with a draft of composing topics and asks the community for amendments as well as willingness to contribute. Once the list of contributors is established, it will be possible upon request to the website administrator:
1. Allocate the needed role to the list members to enable them to write and edit pages
2. Create a specific group of the contributors to facilitate their interaction through GossyForum.
There might be subject for which the option of alphabetical order would make more sense. I have not yet clear idea about that so far.