I think that we will never see a new coin to replace bitcoin and Ethereum. Because bitcoin is the world's first cryptocurrency. And nobody will displace it. As for Ethereum, Ethereum is supported by many projects ... And each project ICO produces tokens on the basis of Ethereum!
ETH is on the 3rd place already. And if team will not make something valuable for own project it can be far from today. One of the big ICOs Tezos recently sold 82k ETH. Do you think they believe in ETH? I think No 