So the main question is... why? The closest you get to this sort of thing in practice is something like a parser generator, or an automatic interface generator

So the main question is... why? The closest you get to this sort of thing in practice is something like a parser generator, or an automatic interface generator. ANTLR and Tree-sitter both allow generating parsers in a variety of languages, but their input is basically a description of an AST in a highly specialized and extremely declarative context. Once you start having actual logic in your code generation, there is very little benefit to codegening to a high-level language instead of going directly to a compiler IR, a bytecode, or assembly directly. The places where you see that happening--JavaScript being the biggest one--is largely limited to where there is no other alternative.