Vega uses the same technology as the current Polaris - except for the use of HBM memory instead of GDDR.
It's more the "next generation of Fury" than "the next generation of Polaris".
Think "Fury/FuryX/Nano" vs "R9 390/390x".
The RX 490 (if it actually appears) still looks more likely to be a "dual Polaris" card than anything else.
Architecture is not the same. These are the latest information on the architecture:
" Lets start off with a simple summary of Vegas key features. This should help paint a picture of how much of a drastic step forward the new architecture is compared to Polaris.
Vega Architecture
4x Power Efficiency
2x Peak Throughput/Performance Per Clock
High Bandwidth Cache
2x Bandwidth per pin
8x Capacity Per stack ( 2nd Generation High Bandwidth Memory )
512TB Virtual Address Space
Next Generation Compute Engine
Next Generation Pixel Engine
Next Compute Unit Architecture
Rapid Packed Math
Draw Stream Binning Rasterizer
Primitive Shaders " .