It seems like any sufficiently detailed specification is pretty much already code or is trivial to translate into code. A language for providing those specifications to a synthesizer would likely balloon into a full-blown programming language, defeating the entire point of this approach. At that level of complexity, a synthesizer just becomes an especially aggressive compiler.

That said, maybe there's a need for something like that. A programmer could write an exceedingly thorough set of unit tests and let the synthesizer worry about how to satisfy those tests. Writing tests is almost universally simpler and easier than writing implementations. I can see the potential productivity enhancing value of that, especially in situations where I have to work in an unfamiliar framework. Like I might not know how to write an Electron app, but I could certainly write the unit tests to specify the front end behavior I want. A synthesizer could save me from having to learn all the nitty gritty framework specific techniques. Basically TDD without having to do the actual implementation. And eventually if the application required performance enhancements, a developer with the correct expertise could tune my synthesized code.

Because, right now, developing specifications is by far the hardest part of coding. But implementation is still not trivial in most cases. For certain use cases, it might be helpful to free up developer time to focus on specifications and QA instead of feature crunching.