Please remember that these are still rumors, and to take with a grain of salt. I did include a few more things I was told, but that have already made the rumor rounds (Typhus and Cover Saves).
via Grant (This post has been updated with corrections)
Corrections and Details
Plague Marines do have FNP and do not need Typhus for it
Typhus does give FNP to Cultists and they are fearless when upgraded to zombies.
Lucious the Eternals attack profile is based on the WS of his Opponent only in a Challenge
Daemon Forge is an optional to use ability that is only for shooting not CC. It allows to re-roll failed armour pens or to wound roll, but you have to roll a d6, and on a 1, your defilier looses a hull point.
Non-corrections
Typhus unlocks plague marines as troops
Cover is definitely 5+
The book is called chaos space marines.
There are no legions.
random terrain is officially called "mysterious terrain"
the anti psyker stuff in the book is a special rule called "suffer the witch". Every unit can negate a power on a 6 up but it can be buffed....
One is called ecstasy...which sounds weird but basically it allows the user to fire his weapon at his strength value.
Another special rule is called soul blaze
Some usr names in the codex are "strike down", "blind", and "un-weilding". these are in chaos marine entries, with rules in the main rulebook
There is a usr called "invisibility" that seems to have an affect on targeting a the unit and also effects assault.