With the introduction of private idea portal comments, these comments can be made visible to all, or only to the comment creator and internal users. However, internal users may actually be a very wide audience and it would not always be appropriate to have comments visible to this audience.
It would be useful to have another option to make private comments visible to Aha! users and the comment creator
+1 on this from my org. Internal users for us could be >100K employees and so we need to have a more restricted channel between the creator and the Aha user.