The author's origin story compares bash and Python. But then there are python-based shells like xonsh, why wouldn't it be better to improve those vs having this new one?
The biggest difference between NGS and other shells is the UI. It's work in progress. Ideas are at https://github.com/ngs-lang/ngs/wiki/UI-Design
Another big difference is that NGS is a language designed ground up for DevOps-y tasks. The result, in my subjective opinion, is clear and concise scripting. That's due to better fit between the language and problems being solved.
Edit: Python for example "doesn't like" functional programming, while NGS supports it and using map() and filter() is idiomatic.
Edit 2: explanation why UI takes so long. That's because it is being implemented mostly in NGS itself so the language must be in shape (and now it is but it took time).
It is not for someone that wants a shell but for someone that wants a Javascript repl...