All good questions.
I really get the feeling Zen is going to be essentially Broadwell without terrible scaling issues; or essentially clock similar or even higher compared to skylake but without the arch/ipc improvements (and ditching the built-in graphics should allow them some space to clock cpus higher in a similar tdp). One would think this would be something like 2x65w (140w) chips on a package, but who knows.
In a world where Broadwell didn't *appear* to be an enthusiast IPC/single-threaded disaster (made up for on the desktop through gpu upgrades almost nobody cares about), it would be interesting to see 8-core parts battle it out at similar clocks (4.2ghz?). As it sits though, one has to wonder if wonder if Intel will bring something like 2-4 extra cores at a lower clock to the enthusiast fight, while AMD could bring a higher core clock on the 'midrange' desktop to play against Skylake.
I could be totally wrong, but I envision them doing something like set tdp aims for both chips and mcm packages (ex: 35w, 65w, 95w, CPU; 30w, 60-65w, 70-75w etc gpu) and then mixing/matching it with either a single cpu chip, two cpu chips, or one cpu + greenland gpu clocked in different configurations (ex: 65w/95w/140w etc)...but it's also conceivable they could be arbitrary and very much dictated by whatever it takes to match/beat Intel (or even a low-end nvidia gpu) in whatever metric a certain product is aimed (or is the most efficient mix hence showing them in their best light).
It surely will be interesting to see how this all develops...but I think such a slotted approach (especially from a binning perspective) would make sense, as well as could explain why one such apu is rumored to have an extravagant tdp...It could essentially be the 'top bin' of both cpu + gpu chips (ex: 95w cpu + 75w gpu).