This should be a pretty simple suggestion (although I am not sure how simple it would be to implement).
There are some questions where the question and answers will be the basis of pretty long and active comment threads. I think that this should be used as an indicator of the Question's Hotness.
I would imagine that incorporating it into the Active might not be a good idea, because if I understand correctly, the active list is generated based on whatever made the last contribution, whether it was a question, answer, or edit? Perhaps this should be kept solely for the HOT (not Active) calculation.