I know that they aren't supposed to be able to do this, but with some thinking I think I may have though of a way to do it.
My nonsense (probably)
The addon would tell what class you are (they can do that), what spec you are (they can do that), then based on the amount of health lost from raider x suggest a spell that won't over-heal them in the tool tip/box? Even if the addon had to supply itself with names and ranks of spells, this seems possible.
Is it?
Sorry if that doesn't make sense