Hello,
Ideally we should keep users that pretty much have a profile picture and they are active.
If they have pictures but they are inactive, we can still keep them to fill an space and make the site looks nice.
But if we have an inactive user without profile picture, it is useless, from the search perspective, appearing a profile without picture.
If you guys add a "Picture Count" and "Last Login" to the users area, it will be easy to identify those users and in order to delete them:
PS: Thank you for 4.0 update, pretty cool features!