According to the ETH dev call, the ProgPOW is a launch for July. So the RX 580 might have a useful life once again. Even though the ProgPOW seems to favor Nvidia's if the ASICs are eliminated from the network, maybe the profitability will go up to be marginally profitable and we might see $1/day/GPU of profits like the good old days.
The only issue with the 580 is if it has 4GB memory and those are already running into issues. My Windows 10 rigs had issued and I had to either switch to Win 7 or Linux. I wonder if we will get this issue with ProgPOW.
Regarding selling and buying Nvidia 1070, you are going to take a huge loss on the RX and pay a large premium for the 1070. There is huge demand for the 1070 due to gamers and almost no demand for the RX series.
Even more reason to dump the 5x cards either for what some are suggesting a 1660ti or 1070ti , of course if you already have the polaris card keep it I suppsoe and wait but please do not buy polaris cards for mining