Hi Andrew - I believe there may be a long term plan to implement this ability at some point, but it's not something we've moved on yet, since we haven't received a lot of feedback in favour of it yet. There's also some hesitation, because there isn't a super straight forward way from a UX perspective to make a deleted lead record recoverable if it's accidentally deleted--which we run into from time to time with resetting conversion stats already.
Right now, most of our customers are content with being able reset their conversion count if necessary. And for the most part, folks are either using email notifications to reach out to leads as they come in (which means having old test leads stored doesn't really matter to them) or they're downloading all of the data as a .csv and already planning to manipulate that, so they just delete the few test leads in their data.
Again, that doesn't mean we won't get to it eventually, but we do try to prioritize development based on demand, so there are quite a few things ahead of it in our queue.