> it's the worst of both worlds since it's neither portable nor that much better than POSIX

Writing modern bash using the updated syntax, it is easy to make robust scripts and the syntax around things like quoting is simple and consistent.

It seems odd to me to suggest that one should either stick to the old brittle /bin/sh syntax or not use bash at all. It has it's place in the world and it should be done the modern way.

You'll find 10s of thousands of lines of bash in the kubernetes repo and all the files I checked are written using modern bash syntax. There must be a reason they choose bash for these parts.

Of course, in any case everyone should use the tools they like and find most suited to the task at hand.