In Commerce 1.x we had to use Commerce Fancy Attributes and Field Extractor to render attributes as a different kind of value beyond its label/title. Such as showing a color swatch instead of just a color name.
Now that we have commerce_product_attribute_value entity, we can implement this in the core module.
Add an option on the Edit form to select what field to use for the add to cart form. Render that fields based on the display mode settings for the bundle.
Write the patch.
The way to configure the display of the field seems rough on UX. But that can be improved in time in a follow up.