It has been rumored that AMD’s RX 500 series graphics cards will be rebrands of the current RX 400 series. So we’ll see the RX 580 take place of the current RX 480, the RX 570 in place for the RX 470, and so on. Rebranding means that these cards will be based off the same silicon as the previous cards. It is speculated that the rebranded cards will get a slight bump in clock speeds, but nothing significant.
The new RX 500 series is expected to launch with the Polaris 10 based parts on April 4th, with the Polaris 11-based parts coming a little later on April 11th.
AMD does have a history of rebranding their graphics cards every year. While this is disappointing, it is what AMD does.