The incompatible syntax of fish makes it a no go for me.
As an SRE, at my day job I often need to copy/paste commands that are generated from a playbook.
Our playbooks use Bash, and in practice Zsh is compatible. But a co-worker using fish often has to manually modify commands before running, and I'm not about that life.
The problem with fish is mostly the different syntax for setting variables and lack of heredocs. Sometimes the string substitution differences come up too.
SRE running copy pasted commands directly instead of a script or some automation solution? I don't think the problem is the shell...
If you want to know if an application is running, implement health checks. I hope I never have to deal with the pattern suggested in this article in a production system.