The RX580 was always "sold" as an updated RX480 by AMD. The GPU chip is Polaris 20 vs Polaris 10 (in RX480). Just a few tweaks and a speed boost.

The days of 50 percent improvement per year are gone. Now, chips only improve about 10 percent per year.

Need a new chip design to get a real jump. And, truly new designs take 2 to 4 years to produce.

That's Vega. AMD is "selling" Vega as the next big thing. Nothing official, but I'm expecting roughly 100 percent better performance than RX480 (in DX12 graphics benchmarks -- games can be CPU limited) -- for a price (to be determined). AMD Vega arrives in 6 or 7 weeks

Long term, AMD Navi in 2019 (??) is a whole new approach to speed. From what the rumors say, it seems feasible to get "virtually unlimited" speed boosts with the AMD Navi concept (at a lower cost per FPS). But, that's 2 years away (or more) -- at least, there is something to look forward to after Vega