Paragraph Rules, Borders, and Shading are all great. They are also all: flat, uniform...boring...

Sometimes a layout demands stuff that is more...messy. Clients often ask for 'grungy' effects to highlight specific parts of text, and every designer gets what they mean.

I currently use an anchored image to achieve this, but it's fiddly, and easily broken. It requires scripting or tedious CandP.

Adding an IMAGE option to Paragraph (and Character?) styles would be brilliant. When I'm working on webpages, I'm using 'background' in CSS all the time.

https://www.w3schools.com/cssref/css3_pr_background.php

That same flexibility in InDesign (image link, position, size, 9-slicing{?!!}, color modes, etc etc) would transform the print/pdf workflow immensely.