I think that Bitcoin will remain the main cryptocurrency in the world. It is digital gold. But the ethereum has a lot of competitors. The team of ethereum is very slowly updating its platform. Perhaps EOS or Cardano or NEO or another blockchain will replace ethereum.
I don't think that Ethereum will be replaced by other platform such as EOS, NEo or Cardano. They may be quite slow to finish their update process but this thing is needed to guarantee everything works smoothly because Ethereum is almost the biggest platform in cryptocurreny world, so they can't be hurry to make mistakes