Ah nice! Well, hats off this is really impressive. As other commenters mentioned the extent to which it's documented and the restricted scope probably helped.
Amazing work. I'm interested in the choice of WASM - presumably any target that can run DOOM could've been used? Of which there are innumerable choices I assume. Was it for symbolic reasons or genuinely the most useful target?
You might be right that they're similarly powerful. In some cases, an arbitrary output format might in and of itself be desirable. Like it might result in token savings or be more natural for the LLM. For instance, generating code snippets to an API or plain text with constraints.
And this is more esoteric, but technically in the case of JSON I suppose you could embed a grammar inside a JSON string, which I'm not sure JSON schema can express.
FWIW, llama.cpp has always had a JSON schema -> GBNF converter, although it launched as a companion script. Now I think it's more integrated in the CLI and server.
But yeah I mean, GBNF or other structured output solutions would of course allow you to supply formats other than JSON schema. It sounds conceivable though that OpenAI could expose the grammars directly in the future, though.
Similar approach to llama.cpp under the hood - they convert the schema to a grammar. Llama.cpp's implementation was specific to the ggml stack, but what they've built sounds similar to Outlines, which they acknowledged.