Bitcoin will not be able to remain the first until it increases the speed of transactions at least to the level of ether, in the store you can make a payment in 15 seconds, and in half an hour in any way
but ether was not designed to become a payment method, ethereum is a smart contract platform, bitcoin is a base layer protocol
in the near future we will see what crypto payment coin/protocol will have a mass adoption
ethereum itself will not be, mybe some other dapp build on ethereum ofcourse, but there are lot of dapps platforms where you can build your crypto payment solution