The details align with what was previously reported on these "Polaris Evolved" graphics cards. There is immediate availability today on at least the RX 580 but have yet to see the RX 560 or RX 570 available yet from any Internet retailers.
On Amazon they have several RX 580 cards available as of the top of the hour. With not receiving any RX 500 review samples from AMD, I just bought the MSI RX 580 ARMOR 8G OC GAMING Radeon RX 580, which launched at $239 USD. This MSI RX 580 card was the cheapest I've found so far today for having 8GB vRAM as really wouldn't recommend a RX 580 with only 4GB of video memory. I went for one-day shipping and have already been working on comparison benchmarks the past few days atop the latest driver code, so by Wednesday evening I should have Radeon RX 580 Linux OpenGL/Vulkan benchmarks to be able to share.
At NewEgg I have yet to find any Polaris Evolved cards listed.
I am still in the process of looking for a Radeon RX 560 but they don't appear yet on Amazon... There's been a number of Phoronix readers mentioning interest in RX 560 4GB Linux tests, so if I find a deal on one soon, will try to get it.
Stay tuned for the RX 580 Linux benchmarks on Wednesday for a nice comparison. If you appreciate all of our Linux hardware testing at Phoronix, consider showing your support by joining Phoronix Premium or making a PayPal tip. Thanks for your support.