As with all rumors, please take with a grain of salt
via Captain Ventris
Sisters will be getting a standard book, but it will certainly be coming well after the Necron book. Talked to my source this last weekend. The WD codex for sisters is simply a holdover till 6th ed. for now. Also its apparently a "filler" codex because the necron book and models were delayed in
Production and wouldn't get released till november (this was apparently decided 6 months ago). The WD sisters codex was rushed btw and wasn't thoroughly playtested... Two waves of Necrons are supposed to be released the weekends of Nov. 12 and Dec. 3rd. What models will be in what release is still being discussed, obviously the codex is in the first wave, but he also mentioned that warriors were getting re-cut with the scarabs removed and options added in their place. Scarab swarms are apparently going to a multi-part finecast kit that is more dynamicly posed than just scarabs hovering in place (I'd already done something similar where my scarabs are actuallt bursting from the ground)
Also on an off-topic note, some minor waves are supposed to be released for various armies with 6th ed. One of note that he mentioned was a new eldar jetbike kit with parts to make either 3 guardian jetbikes or 3 Shining Spears.
Take with whatever salt you feel is necessary.