Definitely is a core feature of BAML. My main complaint with BAML is that it’s all or nothing. It’s very opinionated and we can’t get the benefits without the DX and vice versa. Separating this feature without requiring a DSL of model definition is a great add.
TOML has some readability and compactness benefits over JSON while still being both common enough for models to easily be able to process it relatively reliably and widely supported in most languages. I suspect BAML still performs better but likewise due to the tooling work I haven't integrated it.