What problem does this address?

This came up as part of the FSE Outreach Program's All Things Media exploration:

The ability to add multiple background images to any block. This has been available in CSS for years and would provide a creative lift to WP.

What is your proposed solution?

While currently work still needs to be done to enable a background image in more places (different examples: #14744, #38436), it's worth considering what the option might look like to have multiple images layered as is done with CSS.