I was building a similar function for @exxp back when we still had a 1m SP delegation from Steemit. Mainly to determine which of the guest accounts who signed up with email / social media profile we should gift free accounts to.
I think another good variable to have is the diversity of users people comment in response to. Quality is of course important, but also engaging with different people and not only the same users over and over is good for platform growth and user experience. Especially when quality is still a requirement so that users actually have to take the time reading a post in order to make a thought-full reply to it. Thus, this helps incentivize users not only to write thoughtful comments, but also to look for and connect with new users making interesting content.
Imo, incentives should be best aligned with a growth strategy. So it should correlate with behaviours that promote growth. Such as looking for and engaging with new people (also helps improve user retention when new users are more likely to receive a thoughtful comments this way).
Thanks for running this project and curaying engagement:).