Plastic Sisters have been rumored for a solid 10+ years now. I'll believe it when I see it.
That said - Harlequins was a pleasant surprise so maybe they WILL finally get their relaunch like they've deserved for years.
Who really know what is really coming this year for 40k now that the codices are all out. The only thing I think most are expecting is another campaign box set like Sanctus Reach and Shield of Baal; however, beyond the generic "we'll probably get one of those" who knows what we'll be seeing in the coming months.