Lack of visualization ability to see the connections between concepts. One child element in canvas could have the logical parent or be a parent to elements from other canvases. To effectively see connections and make conclusions from this, information should be presented as clearly as possible. It seems like 2d space is pretty limited.
Just use the most natural for the human brain 3d space. Present canvases as colored clouds with elements - which float around and turn to the user when you click on this cloud. When you’re in the 3d space you can see, form and follow the connections between subjects, forming some spatial intuition about topics in your brain along the way. Then you can dive into the specific topic, by double-clicking cloud and opening canvas. Wouldn’t it be cool to have some Tony Stark-style note-taking solution in the app?
There is already a 3d graph view plugin, but it doesn’t allow working with, presenting, and organizing information in such a cool visual way as the canvas feature.