Canvas looks strikingly similar to this (almost exactly the same aesthetically), and I'm curious what the "killer feature(s)" are which give it an advantage over Paper, which is developed by a much larger company (Dropbox).
I haven't been that happy with Dropbox Paper though. It doesn't handle basic things like bullets in indented blocks, or line/paragraph breaks in numbered lists. Hackpad (Dropbox acquisition) didn't look as nice, but had more functionality. Now Paper is replacing Hackpad.
I'll be giving Canvas a try.
For example, right now in a Google Doc if I want to connect it to a Trello list I need to add a bullet for each card in the list, make it a link to the card, and keep both things in sync. What if I could just drop in the whole list (or even a whole board in some cases) and have my project plan and my specific cards in the same context without jumping between different tools? That's a killer feature for me if they can pull it off.