This is our most requested feature - and here it is! Please note that v1.2.0 features are rolling out slowly, and this layout is not final.
You can start a conversation by going a user's profile and finding the text "You haven't started a conversation with (username)" and clicking/tapping "Start a Chat"!

If you have already started a conversation with a user, it will show the most recent message with a button to reopen the chat!
You can also access conversations from the menu!

Along with this update...
Since the input for commenting is reused for direct messaging - many upgrades that came along with Direct Messaging are now available for commenting! Such as, the text formatting menu and multi-image support!
Enjoy! :)
This update is possible due to the awesome people over at Peerboard, check them out!