For what it's worth, there are a lot of good interesting languages out there that aren't Python and have pretty good library ecosystems. Kotlin, Elixir, and Elm come to mind. But they don't exactly fit the Python niche.
What you're describing sounds to me like a modernized Common Lisp with commercial backing. Rework CLOS a bit, clean up some of the other crufty old weirdness, and give me a big selection of high-quality well-supported libraries like Numpy, FastAPI, Trio, etc.
The advantage of doing it in some Common Lisp derivative is that things like React JSX are pretty much "free" and wouldn't much seem out of place, whereas in Javascript they need a whole separate build/compilation step and are often portrayed as black magic fuckery.
edit 1: Arguably Julia could be used for a task like this, but its library ecosystem and language runtime are heavily skewed towards numerical computing and data analysis.
edit 2: Raku also sounds like a possible candidate here, but it obviously lacks widespread adoption and last I heard it fell significantly short of Perl 5 performance. I'm not sure what kind of library ecosystem it has nowadays and I doubt we're going to see big commercially-backed library development efforts for it, soon or ever. Perl 5 has a huge ecosystem of course, but it's such a nasty warty language with nasty warty tooling.
