Show HN is for things that can be tried now so you could post it as a Show HN after you're past the pure spec phase or as is but without the Show HN - take a look at https://news.ycombinator.com/showhn.html
It can be tried now. The linked reference implementation (https://github.com/jmillikin/go-idol) has a working schema compiler and code generator, with the Go codegen being rather MVP-ish but still functional enough to bootstrap itself.
Somehow I got to "The following features are planned before Idol stabilizes: At least one complete implementation of the specification [...]" at the bottom and missed the link near the top, my mistake.