This was floating around over on 3++ and while some of it duplicates other rumors, there is some new stuff in here as well. The one thing that seems to be a constant, is that many people are claiming and maintaining that the codex release will be set for April.
Some more bits of information were floating around over on 3++. Please remember that these are rumors, some salt is always required.
via 3++ is the New Black (from inside the Chatbawks)
option to have all units with 6" fire overwatch - lots of dice rolling, little effect FTW
Fliers are AV10/11 with 6x S6/7 shots at BS3; not twin-linked
there is a tank commander
Tau vehicles can no longer fire as fast vehicles (i.e. multi-tracker upgrade gone/changed)
Riptide - name of ubersuit and is an Elite choice.