In order to have any advantage from this, you would have the added complexity of splitting your file format into tables that can be queried in a useful manner. However, for an image file format, you most likely need to hold the entire definition in memory at all times anyway. Assuming that’s the case, doesn’t XPath get you there most of the way (assuming XML), with _way_ less complexity?

Image data is just binary blobs. You aren't splitting that into channel columns or anything. But an image file for an editor like Gimp isn't one image blob. It's dozens or hundreds of them - one or more per layer - along with tons of associated metadata at every level.

All that tends to fit sensible schemas and managing it is what SQLite shines at.