Yes, that would be an option, but I lean more heavily towards "less is more" and minimalism. A drawing canvas is generally like one of the beginner textbook example projects for HTML5 canvas stuff. The only possible source of complications is UI accommodations for mobile.
Maybe 480x360 might be more workable for a canvas, as drawing to a square might be weird.
I think just a flat non-layered raster is all that's needed. A bonus feature could be some basic animation option (like up to 10 frames or something) that'd maybe export to an APNG or whatever format is stable/workable (or just plain ol GIF), which I'm sure would be like crack to animators (given Flipnote or whatever was popular in previous years for that).
