Based on my opinion, I dont think that there's an existing coin that can possibly replace bitcoin in the next future because bitcoin has still a good potential so it is impossible to replace.
We don't know what will happen in the future. now many platforms already developed their own blockchain. We also don't know and think network blockchain this can be as good as the ethereum and widely used one. There is now a eos began to grow. for now the bitcoin main remains, for the future we all no one knows it.