I thought oil shell was the hot new thing. I really think it has the potential to displace both bash and zsh.

My impression has always been that zsh is where cool new features go first, and then bash plays catch up. I remember longing for associative arrays in bash while zsh and ksh already had them. What finally got me to move to zsh was colorized syntax; it makes some of my typos very obvious before I press Enter. In general zsh is still more pleasant for interactive use, but I still write scripts in bash since it is everywhere.