This has been out for a while now. But before this, what people used to do is create a group with just yourself as a member, and send messages there. You had to create a group with 2 people (yourself and someone else), and just remove them because it could not be done directly. And this could be used as notes or whatever.

Right now I message myself but let's say if one wanted to maintain a separate chat for notes or some other purpose, they could create an infinite number of groups with just them in it and get it working.

Of course I think OP's solution is offering an interactive experience more than just one way communicaton.