Genestealer Cults were originally recently rumored by Hastings, only to be changed to a probable stand alone box set game vs Deathwatch. However, rumors are still being heard of Deathwatch and Genestealer codices. Whether rumor reverb, or indication that there will be a codex release, its still unknown.
Please remember that these are rumors.
Here was the rumor by Hastings.
via Bird in the Trees on Bell of Lost Souls posted by Larry Vela
GeneStealer Cult Minis Rumors
Clampack 1: Magos with classic robe & staff
Clampack 2:Large-cranium figure with arms extended pose
Genestealer Hybrid box: Updated versions of the original plastic Hybrid models. Modern-Genestealer like arms in attack poses, alongside hunam arms with knives, and lasguns. 32mm bases.
Genestealer Cultist box: Rabble humans without obvious mutations. Minor tyranid bits here and there as armor, and some tyranid style weapons as upgrade options.
Cult Truck: A down armored open bed vehicle in the similar vein to the AM Taurox.