This solution could work for other blocks. I encourage theme authors to experiment and use other SVGs to see what they come up with.

This brush stroke style gives me an idea for something. I'm gonna go totally overboard with it though!

One thing I noticed is that with the z-index: 1 on the heading block, if it is located close to a navigation block with a submenu, the submenu is obscured. This is despite the submenu specifying a higher z-index.
Dropping the z-index from the heading but keeping the -1 on :before doesn't seem to stop it from working correctly, and the nav submenu was no longer obscured. At least that's what I found in my limited testing.