Theoretically this should work on every Kinja blog/forum like Groupthink, Clashtalk. TAY etc.
I don't know if a lot of you know, but as authors on the Odeck we have access to this page: observationdeck.io9.com/private which directs you to this page below:
I've numbered all the relevant parts:
1. This is a draft that was written and saved by an author that has posting privileges on the Odeck. The draft is accessible and if you click on it you will be taken to its kinja page as a preview like so:
2. Pressing on all will show you posts, drafts (scheduled and unscheduled) of posts, and replies that appear on the Odeck. The replies I think only show comments from authors and members the Odeck follows as a whole. If anyone wants to shed light on this aspect feel free.
3. Your Posts button shows you all drafts and posts currently on the Odeck.
4. Drafts are just drafts that show you scheduled posts or posts that have been made but not published.
5. Recommendations show any recommendations you have made.
Now I am making this post because I think I may have found a way to have messages. But first 99telepodproblems suggested we let the whole Odeck know so that they go in and delete any drafts they don't want people to see. Now to have a truly private draft this is what you gotta do:
1A. Here is the dropdown menu for all the blogs you have posting privileges for. For a post to be truly private, a draft only you can see, you have to click your personal blog then click 2A, and make it private.
Now you are wondering how the hell can you have limited messaging that no one can see? Well if you click on any draft from the private view of the Odeck you will be taken to a preview of said post, but you can still comment on it. I decided to test this by commenting on some draft that 99telepodproblems had made. He saw the notification and the little blurb but couldn't access the comment because when you click on it you are redirected to this page:
Which effectively nukes any comments made on the draft page. Also when you go back to look at the draft page you don't see any replies that have been made.
Now you can't make verbose messages, because of the notification cutoff, I estimate its about 80 characters, but it still private messaging of sorts.
If you want to reply go to the person click on any of their drafts and make a reply. Now if the person goes to their private notifications on their blog they can see the full comment you made. The private notification page I'm talking about is the whateveryournameis (dot)Kinja(dot)com/private/notifications.
To reply to you they have to comment on a draft page you make. AND pictures and gifs work as well. Now this is isn't completely private as people who go into the private view of the forum/blog will see the comments as notifications, however they only see one side and they can't click on it to see the whole conversation.
Also make sure you trust whoever you are messaging with this way, because they can make the draft pages public and all the replies it has will become public. The replies are logged but cannot be seen until the draft is public.
So if you have drafts you don't want anyone to see go into the private view of Odeck and delete them. If you want to set up a private page where people can leave replies make a page like 99telepod and I did.