Well, I'm reading these statements that next gen must use Zen for CPU otherwise it won't be next gen for quite some time now. And I'm pretty sure that they aren't true as with pretty much every gen since PS2/Xbox the main h/w part of a gaming machine is the GPU and its performance and capabilities. Couple a 20TF GPU with an overclocked 8C Jaguar and such machine will likely be a lot better for gaming workloads than a 10TF GPU + 8C Zen one. CPU isn't this important for your typical gaming scenario.
Simulation is something which usually lands very well on GPU compute and isn't something that you want to run on CPU anyway. CPU is running game logic which is mostly what you'd call "scripted" and isn't very expensive to calculate even though you can always use more power for it if it's available of course. With the rise of new APIs and GPU driven models even the requirement to have CPU feed commands into GPU might go away on the next gen.
When I say the game simulation, I'm talking about everything from the scripted game logic to animation, to audio, to player input, to interactive-physics (not all physics is or can be moved over to the GPU—generally non-interactive game physics like particle effects), to collisions, to AI logic and pathfinding, to network code etc etc.. as well as building the command lists to tell the GPU what to render.
The CPU doesn't just run the game's game's main logic and that's it. It sounds like you're understating somewhat how much of a game's processing workload the CPU has to take on, and overstating how much of that workload can be feasibly ported over to the GPU.
GPUs in general excel in highly parallelizable, non-branchy workloads with very little data dependency. Yes over the last couple of gens more and more traditional gaming CPU workloads that fit this description have been ported over to the GPU, but don't forget that game worlds themselves have become larger, along with gamer expectations for higher and higher levels of interactivity within these larger gameworlds, which invariably will demand a stronger and stronger CPU—alongside a bigger GPU—in order to cope with these types of tasks. As game worlds, rendering resolutions and more performance intensive rendering techniques get employed, higher demands are placed on the GPU, meaning less availability on the GPU for CPU tasks that might be more efficiently placed there; in which case a stronger CPU in addition to the GPU will always benefit games.