Or fish, which is basically zsh with sane defaults.

And a completely incompatible non-POSIX syntax, which sounds great in theory but isn't nearly enough better to justify the departure IMHO.

Why does compatibility matter? If you have a script written for sh or bash it will just run using that interpreter.

For starters, any utilities based on sourcing won't work, such as nvm/rbenv/etc.

That's technically true for zsh in cases, but it's far easier to port or add compatibility for zsh than fish.