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.