The AMD news has been coming out fairly often of late, and today is no exception. A new APU is supposedly in the works that will use up to 16 Zen cores and a Greenland GPU to bring the gaming potential. Greenland was mentioned yesterday as the rumored codename of part of the RX 400 series, maybe the high-end line. However, with this new APU, Greenland and maybe the entire Arctic Islands line will be reserved for APUs, as this new APU is said to use HBM, just like Greenland. As for the capability of 16 Zen cores, this doesn't mean it will use all 16, but could. The new APU may be that rumored HPC APU, but it could also be in the running for a server product. Zen is the codename for AMD's APU line launching sometime next year or in 2017, and is said to have PCIe 3.0 and quad-channel DDR4 support.
It all sounds like the makings of a high-powered APU, but remember all of this is just rumor, and this 16 core APU could just be for the server market. The desktop market would probably top out at 8 cores, but you never know what could change in the next year or so.