Is your feature request related to a problem? Please describe.
We currently have a few inconsistencies with media uploaders, one of which is the dropzone upload/replace flow that exists within the core image/gallery and soon to be Media & Text block. We should consider adding that same drop zone/replace functionality to the Cover block, as it exists in each other instance of media blocks.

Screenshot

Describe the solution you'd like
When dragging an image/video over the left or right area of the cover block (the areas not managed via InnerBlocks component), I can drop it in and the media is assigned as the Cover block's background media.

Describe alternatives you've considered
None, other than having to different edit flow for this block, compared to other image/gallery blocks.