Who is the author of the next upcoming codex has always been an issue, and a hard topic with the community. It has spilled a lot of unnecessary angst towards people, that I am sure is heartfelt by those that work on the books. This is being dealt with by Games Workshop in an interesting way, no longer will the codex have a single author listed for it.
Please remember that this is a rumor, although we are seeing this with the new Tyranid Codex release tomorrow.
via an anonymous source on Faeit 212
Also heard a bit about authorship of codexes, all future releases will be linked to the gw dev team rather than individual authors to alleviate prejudgement of upcoming codexes via leaks.