Vega VII is a 4096 Shader die with 4 compute units disables giving it 3840 Shaders, its the MI50 Radeon Instinct Workstation card, which is a cut down MI60.
This is my thinking.
Top of the line Navi will be an enhanced Vega with a small bump in IPC, maybe 10%, also a full fat 4096 Shader GPU, it will have GDDR6 not HBM2 so a slightly smaller die as HBM2 requires 2X 2048Bit IMC's (one on each side) to one 256Bit IMC, down from 331mm^2 to maybe 300mm^2.
in games that massive HBM bandwidth is wasted, it will not have the huge Floating Point compute power of the MI50 Radeon Instinct / Vega VII, which is 13.4 TFlops FP32, it doesn't need it in games, makes no difference to have a lot less, it also saves on power consumption.
So smaller, cheaper to make and faster, the GPU die its self will be significantly more power efficient tho the GDDR6 memory IC's will bring the power back up again, 8GB of GDDR6 costs about a third as much as 16GB of HBM2, its over $100 less, possibly as much as $150 less.
A faster gaming GPU with greatly reduced production costs, i'm thinking RTX 2080 at £400 to £500, £200 cheaper than the RTX 2080.