High performance notebooks. It can scale down too.
mITX builds. Boutique rigs. Actual PC gaming rig if price is competitive.
My only concern is the pricing due to this rumor of HBM being expensive. If it remains cheaper to go with a CPU + dGPU combo for similar performance, it will not be a good option outside of the aforementioned niches (well, notebooks aren't exactly niche).
Most of us on these forums understand the benefit of HBM. What a lot of people forget is that PC gamers, at least in the way we think of it (not just facebook, pogo, sims, etc) are a relatively small portion of the overall PC market.
It really comes down to notebooks. In the desktop, even with HBM an APU (either intel or AMD) will always be limited by size and TDP, and the necessity to upgrade both cpu and gpu at the same time. Laptops is where an igpu with HBM could shine, since it is pretty much impossible to upgrade or add a dgpu to a laptop.
But again, the market is somewhat limited, and also depends on price. An igpu gaming laptop has to be significantly cheaper than a dgpu model.
And we also have to see how AMD executes. Just because a 40% ipc was mentioned, based on projections, not even actual silicon, AMD fans have suddenly taken that as a certainty. And even if it happens, they have to keep the clocks up as well. Zen APUs have already been delayed to 2017, so lets see when they come out and if they do in fact have HBM. One would assume they will, but one would also have assumed the first Zen cpus would have an igp too, since AMD has been touting HSA, Fusion, gpgpu compute for what, going on ten years now?
My best guess is that AMD will make a moderate comeback in both cpu and dgpu sales, but I dont really think HBM is going to be the huge gamechanger that some do. As another poster said, they really need HSA to take off to make a major comeback. Otherwise, just a guess, but I would say only perhaps 10% at most of the market is really that interested in a powerful igpu.