I think if etf gets approved for btc then btc will become unstoppable and the dream of 100k btc can become reality in one year after etf approval, as far as other coins are concerned i think they will suffer in value in reference to btc value but in terms of usd their value will retain or also grow some what.
I think this is true at first...but then lots of people will expect alts to start picking up and they will use some of their btc to pick up some cheap alt coins, and then we will have a big alt coin rally too