There is a common demand from people for extracting just a very concrete computation from a julia codebase and compiling it to a standalone library (or even just using it within an existing julia program, but guaranteeing certain allocation or real time behavior). For example, julia includes a pure julia implementation of libm, but we also maintain the openlibm C library, since we link it into some of our C dependencies that need good quality math functions. It would be nice just to compile the julia version and have it be a drop in replacement for the libm that can be linked. Of course for that you don't want the runtime, or GC or code generator. The challenge here is coming up with the right interfaces and abstractions to make this a feasible and useful thing, without splitting the community into those that care about it and those that don't. We've started some work in this direction, but it isn't really usable yet.

Yes, for sure my suggestion was an incomplete answer, but still you would want the lower language be GC-aware/GC-compatible so I am not sure what the advantages of having two languages would be compared to having a GC language that can have non-GC modules/functions.

We also have an example of something more similar to what you are asking with Javascript+wasm (or better Typescript+wasm). I think they are both a fertile ground for future growth.