A fairly credible source in the past at the Chiphell forums is now mentioning that AMD might be releasing a new (another) version of Polaris. Polaris 30 would be manufactured at 12 nm and would be 15 percent faster compared to the current RX 570 and 580, Radeon RX 680?

This new info opens up a whole new ballpark of speculation, will there be a Radeon RX 600 series of GPUs based on Polaris? The current generation is built on 14 nm FinFET LPP+. So if AMD moves to a 12nm part, the clocks could indeed be bumped up a bit more, much like what Zen+ is doing for Ryzen 2000.

It's not the first time that this rumor now has surfaced and for now, it is just that, a rumor from Chiphells forum user wjm47196, via computerbase. So take it with a grain of salt. 

AMD Radeon RX rumor: 12nm Polaris 30 in the 4th quarter