... and many also have succeeded. fish would not be as popular as it is otherwise, other alternative shells that break bash compatibility are being worked on and are gaining traction, elvish, nushell, murex...

mixing shells is not as hard as some people claim. it's like switching programming languages. i do that all the time. but then, i avoid bash scripting as much as i can (or shell scripting in general). if you actually enjoy bash scripting then switching may be harder.