This idea would be an extension of the multiple classes adder.
1. Class grouping
E.g. I am a heavy user of OxyNinja utility classes.
Let's say I have a special style for buttons i use throughout the entire website. Which consist of 4-5 classes.
Add new group -> set name e.g. "main button styles" -> add multiple individual selectors like .btn-main .btn-m .transition etc. -> now I add them all in 1 click.
2. Class Suggestions
Basically this would be a small popup/slide-out containing a suggestion panel or just some mini buttons with the class-group name.