I just came with a crazy prediction for Navi: the usage of MCM, Inifinity Fabric and Interposer to make Navi perform head-to-head on all metrics, including efficiency, with Nvidia 7nm offerings.
Take Polaris 10(2304 SPs) and Upgrade it at Vega level of features(DX12.1, HBCC, Primitive Shaders, NCU and etc). Now you do some treatment to improve the per CU performance for a new level. Then you chose the SoC version of GF 7nm(Power/Frequency tables for both 7LP flavors here:
http://btbmarketing.com/iedm/docs/29...ha_Fig%202.jpg). The right choice would be the SHP choice for such a monolhitic GPU, but that's not "scalability".
You shrink four of this evolved Polaris 10 GPUs, use infinity fabric and MCM to tie it all togheter, like EPYC. Then you have a total of 9216 SPs. Then you use Interposer to match the GPU with 4096-bit(a couple of stacks) 16GB or 32GB of HBM3("NexGen Memory"). Then there it is, with an total Area not much bigger Than Vega64 with its HBM2, ready to take on Nvidia's best offering on TSMC 7nm.
Crazy idea, but it looks plausible, no? I Just wish Navi is true GCN2 and not only GCN1.6. I'm enough of minor incremental updates.