What problem does this address?

While editing a details block, if you have multiple details blocks on your page, you can only have one expanded (to reveal the hidden content) at a time. However, there are many times when you might want multiple details blocks open at once so you can see all the content on your page easily and without shifting content north and south as you expand and collapse each block. You can expand more than one at a time when viewing a live page, just not while editing the page.

What is your proposed solution?

Improves overall user experience when editing, especially if trying to copy/paste content from one block to another.