The Canvas is very easy to work with. You can forget about JQuery and everything else concerning the DOM and just write pure JavaScript.
I've even started working on a canvas based text editor.
I did some research before I started and read about Bespin. I don't think they merged into Ace because of the Canvas. It was probably because another team on the same company also worked on an editor, witch had the same goals, and aimed for the same market.
The Canvas is very easy to work with. You can forget about JQuery and everything else concerning the DOM and just write pure JavaScript. I've even started working on a canvas based text editor.