I don't see the harm generally, BUT, since the server is already counting a bunch of stats adding new stats related to others would cause inconsistencies.
I would like to see the old stats archived, stats cleared then some new stats implemented. If the new sub categories are added without rezeroing the current stats then I think the stats will get confusing..
For example, if we added gang kills/deaths now while people keep their old stats then it's not possible to say "40 of [name]'s kills are drivebys" instead we'd have to say "since [date], [name] has driveby'd 20 times, they have killed 100 times since they registered/[date]". If we cleared stats when implementing then it'd be less confusing, you'd just say "Stats since [date]: 40 of [name]'s kills are driveby's".. Hopefully my point is understood