Here's an idea for a new set of badges:
- Conversation Starter (Bronze): received comments from five different people (in total across all answers)
- Catalyst (Silver) : received comments from five different people on a single answer
both can be awarded only once.
Update: for both only count comments on answers, not on questions, because for questions there are usually lot of "did you mean?" comments.
Another Update: it seems that people are worried that most comments would be just pointing out how wrong the answer is. That is a sad (but maybe appropriate) view. I think it can be amended by only counting comments on answers with no downvotes.