This is a vast oversimplification of the problem. LLVM is a compiler IR; nothing more. It is not portable (you cannot generate IR for one target and have it work for another target) and it does not trivially map to the semantics of most languages beyond C.

A programming language is a combination of many components; assembly optimization and target code generation is just one important part of a much larger picture.

I'm only responding critically because I've seen this trope that LLVM is some sort of universal programming language target way too often now. It misleads people into underestimating the scope of the actual problem. LLVM is not a panacea.

If you really want to make your platform programmable from any programming language, invest time into a well designed C API. Your users will thank you.