It appears that AMD will be sticking with an 8-core dies as far as the fabrication of Zen processors in the Summit Ridge platform is concerned. The mainstream desktop platform is expected to feature 8-core and 6-core variants with SMT and will not, initially, have any quad core or dual core options.
I really hope that Microsoft releases support patches for it for Windows 7 and 8.1 (note how they have been silent in confirming this, unlike their stance on Intel chips...). though one part of the article does make me think it will:
Zen will be using a scheduling model that is similar to Intel’s and it will use specific hardware and simulation to define any needed scheduling or NUMA changes. It will also be ISA compatible with Haswell/Broadwell style of compute. It will bring various compiler optimisations, including GCC with target of SPECint v6 based score at common compiler settings.
So, fingers crossed, the 80% or so of the market not using Windows 10 will not be locked out of the full performance ability of Zen.