Tom's Hardware had a chat with AMD CEO Lisa Su about the firm's strategy in the graphics and processor markets, you can read it over here. Among other things, Su mentioned that AMD will be moving to a new FinFET process in 2016 (14nm?), and that this will potentially result in a 2x energy efficiency improvement versus previous-generation 28nm GPUs. Su also mentioned we'll soon hear more about how HBM fits into the company's overall graphics roadmap, and stressed that the new Zen processor design is the foremost thing on AMD's roadmap where the company absolutely has to suceed.
Both AMD and Nvidia, among others, have talked about and been working on implementations of stacked memory architectures, but AMD will be the first to ship. Lisa Su said that it's been in development for a long time, and the decision to put it into production now was predicated on both the necessity and fit for a high-end graphics part, and because the volume shipments expected with the new GPU should help push HBM down the cost curve so that it's applicable to other implementations and products. Surprisingly, AMD made this decision 18 months ago, Su told us.
Su would not comment on when we would see other HBM implementations, nor on which products, but she said that there are neither production nor technology limitations, just decisions to be made "based on the company's overall product roadmap, and individual market decisions." AMD has said that there would eventually be an APU with a high-bandwidth memory implementation. It just hasn't said when.