I think this need derives from user's natural desire to have direct messaging. Like any other social platform, Steemit should have an "official" way to send private messages to other members and groups. "Followers" could be just one of the group. Unifficial Steemit chat, Discord, Skype, WhatsApp does not count because none of them guarantees that the user can be reached that way. Besides you would not even know the user name of the person on that platform which is not the same as on Steemit. Even Steemit chat is completely different and has different user names.
This is quite possible and not hard to implement actually.
I also think that it should not be a part of blockchain. Private chat should be outside of the blockchain and therefore no voting for private chat messages.
I think Steemit should catch up with pretty much every other social network in existence and implement official private chat.