Everyone talks about the fact that Bash is what it is because it is first and foremost an interactive shell, but nowadays some design decisions are just inexcusable in my opinion, like the awful syntax of common programming constructs, the if in particular, that would only benefit from following how every other language works even if they aren’t meant as shells.
Some also argue against the non-modularity with the fact that you should use it for only quick and easy stuff, but that’s just an excuse, if the language runtime that comes preinstalled in your system had modern features and sane syntax you would stick to that and save yourself from installing Python/Ruby if they’re not needed; and it is clear that there is a need for modularity, otherwise plugin managers wouldn’t exist, many swear by downloading the scripts directly and sourcing them in the name of “KISS”, but that is just silly when there is a good system set in place that makes it actually easier to manage it all.
Then there’s the issue of the holy pipelining, that has more or less been overcome by some languages already, this example in Rust shows that it can be easy, so there’s no reason why a terse scripting language couldn’t achieve the same.

In the end I don’t know what’s holding the landscape back, I noticed Xonsh that looks very interesting, but I never tried it, I wonder if it is POSIX compliant and if that aspect even is so fundamental to the success of a shell