Ethereum won't last long. As soon as someone will provide users with better technology they'll switch, as the important part of using Ethereum is using other based-on cryptocurrencies. For bitcoin, tho, because it is first and is the most recognized one, the future shines bright. Especially with the trend of illegalizing ICO's.
True, ethereum now a day is just an ICO platform. They have huge demands because of this start-ups ICOs, I do think that Bitcoin will still on top and ethereum losing their track after Bitcoin since Bitcoin can have a smart contract on its blockchain the same way as ethereum making Bitcoin holders to use that contract and no need to move on the ethereum platform. Aside from that, there are emerging new technology that will render ethereum obsolete or let us say a secondary choice.