Think about it this way.
You are better off buying AMD RX right now even with these small hashrate drops than you are buying NVIDIA right now which doesn't have this issue.
Because by the time the hashrate drops 30%, most of us won't be mining anymore.
Its better making $6/day NOW but paying half for a GPU than making a similiar amount but paying double for the NVIDIA GPU.
Because by the time you ROI that NVIDIA we all will be making $0.25/day with our GPUs and the hashrate drop won't mean much.
But the AMD people will come out ahead since the GPU was paid for multiple times and not the NVIDIA people.
Where are you going to get an AMD RX for half the price of an nVidia card? The main vendors (amazon, newegg and bhphoto) are already gouging on the price on 1070's a bit. When the AMD cards hit the "shelves" they are going to be priced substantially higher because these companies know what they are being used for and know that people are going to pay the price to get them.