I frequently want to say "If you made a certain change to this answer, I'd upvote it". But I don't say that, because it would be a lie, because how would I remember to come back and check?
So how about introducing the idea of a "conditional upvote"?
It could be associated with a comment, so when adding a comment to an answer, you could check a box to say "Conditional upvote". The comment then explains what changes would need to be made to the answer in order for it to qualify for an upvote from the commenter.
The significance would be that I'd be able to go to my profile and see listed all the outstanding conditional upvote comments I've made, and I'd get a notification when the associated answer was edited.
When I upvote the answer, or if a week passes, it disappears from my conditional upvote list.