I've found that the armies people are most excited for which do currently exist in some way are Chaos Space Marines and plastic Adepta Sororitas in that order, though that might just be my area. The (super)human side of 40K Chaos needs a lot of plastic love for the basic kits - Chaos Space Marines, Terminators, the cult units, etc - and I'm glad that plastic Rubric Marines have been confirmed for late 2016 by both Lady Atia and Sad Panda. Plastic Sisters of Battle though....it seems more and more like an inevitability as Games Workshop are definitely aware of the demand, and they can't hide behind the excuse of not doing Dark Eldar-scale releases that often when we have seen three brand new factions for Age of Sigmar introduced in the span of roughly half a year while the Adeptus Mechanicus preceded them by a few months.