Last I heard was around the start of the year, when Jason Hardy was on the Arcology Podcast and said the rigger book would be out about a year from then.
It looks like Data Trails is next (Gen Con release? We saw art from it
here), then the augmentation book (Chrome Flesh, according to a 25 April post on the Shadowrun FB page, maybe sometime this fall?), then the rigger book (I haven't seen a title yet, but early 2016).
I agree: Riggers needed more love in the CRB than they got. And I've always thought the coolest thing about a rigger was driving around a vehicle that isn't "stock".