We'll see if we can revisit this once the 4xxx series hits the market.The release of the new mobile Ryzen CPUs should be quite exciting once they are released and I look forward to seeing some reviews of them if you can get your hands on the hardware.
I would think when unplugged you will have the 15w configuration option for those with iGPU to extend battery life which would make these laptops rather useful for full gaming when plugged in with the discrete GPU and then rather good gaming with iGPU on battery. That is what I would hope for.We'll see if we can revisit this once the 4xxx series hits the market.
One thing to keep in mind is that in the 15W class, you're going to be relying on the iGPU. In the 45W class, the iGPU will be fairly irrelevant as virtually all AMD based machines will have a discrete mobile graphics card baked in at that power profile.