I would say it's not a priority. There is a working C backend, and as long as the LLVM backend does not provide any substantial advantage over C code generation I would say the llvm pipeline is just an alternative. Also when the llvm pieline is the only pipeline nim will be limited to the platforms supported by LLVM which is a subset of languages that are supported with a c compiler.
So I wouldn't see this happening in the near future, but when there is an ambitious community member, it might happen.