Has there been any discussion of defining theme templates via some sort of config file?

I really love how easy it is to define InnerBlocks templates with a data string:
https://github.com/WordPress/gutenberg/blob/ae327b22d6c1fd563290fbc304ea977b1f71480e/packages/block-editor/src/components/inner-blocks/README.md

Then all that extra markup can be abstracted away...