What problem does this address?

Setting up a multi-column query block layout will generate a lot of empty areas:

Masonry layouts are the best way to avoid this and are extremely common in themes...

...and in external blocks (Gosign – Masonry Post Block for instance):

What is your proposed solution?

I would like to see an option next to the "columns" setting to give the layout a masonry style:

There is a related discussion in #25462