ETH currently has 266,000 GH. So that is equivalent of 8,866,666 RX 570/580 cards. Imagine if they went PoS. The current XMR network (500 MH or so) has about the what would equal 62,500 570/580 cards on it. So if let's say only 200,000 of those ETH cards when to XMR... XMR would be much less profitable to mine and you would still have 8,666,666 cards to still spread over other coins...
Well, not all of the miners will continue. Many will sell their rigs since profitability on other algos is not that great.
Until other big players look at the value proposition and decide to full on compete with Bitmain we are stuck.
Exactly. It seems however that it requires a lots of cash to develop and produce an asic chip. Buying off one of their top engineers would be the best option.