What problem does this address?

Right now, if you want to add a cover block to your header, it's a fairly painful experience requiring you to add a Cover block above your content within the template part, setting an image or background color, and then add a column block to separate out the Site Title, Site Tagline from the navigation block before adding in the content you want.

Here's a video of the current experience using the TT1 Blocks theme and Gutenberg 10.1:

https://cloudup.com/c1p8v_ybzp1

This was first brought up as part of the FSE Outreach Program here.

What is your proposed solution?

cc @kjellr this might be neat to explore as a theme pattern. Otherwise, making it easier to add a cover block to a template part and/or set a background image for a template part seems like a good alternative!