Good call on adding this, @frrrances. A few questions:

1. I think this may be defined somewhere else, perhaps since you started work on this, can you double check that there isn't a rule that already does this.
2. Should we be more specific with this use-case? I could see a bit down the road needing to size/align icons in different ways (the "add a component" buttons come to mind) that just this (inline and to the left). Regarding 1) above, I may have created a rule for a class of .icon-inline, maybe extending/proofing that would be the way to go.