ooh, this is great, lets hope there's some adoption.
Im quite happy with just a few additions to basic markdown, however I've been holding off using canvases much because they're not portable, should Obsidian turn to the dark side so perhaps im missing out.
I'm not using them either, but initially had planned on using them for an audio-play I was working on, as a brainstorming tool, in form of a digital board, where I could "pin" notes in different groups and link them (with digital string :D).
Like, there could be a group of notes, each representing a place. Then there could be links to all the actors, that are in this place, to a given time, and so on.
Canvases as a visual index/MOC to collect notes on a specific topic. That’s my main use.
I have used them as a cork board for notes when planning writing (much like Scrivener). I’ve even got templates that have images of an index card to type over.