All of those things have been built before, you're even referencing existing languages that have those "features". Parent seemingly was asking for people to build something completely novel, that doesn't have any FOSS code available that done that thing before.

And yes, LLMs/agents can help you do it for sure, I'm currently building the lisp of my dreams in my freetime, and already have compiler, interpreter, UI framework and some other things already done in a way I'm happy with.

Yeah, the "novel" bit is about integrating all those aspects into one language.

And trust me, such a language that captures enough mindshare is absolutely needed. People thought Rust was going to be it, but it got taken over by the idea of it being the next C++.

IF LLMs are what you make them out to be, it shouldn't have been long before we saw serious attempts at such languages, but I suspect LLMs are of barely any help here beyond some basic implementation tasks.