I, for one, actually like the Canvasing ideas on songs. To be honest, I wish there was more as I have my phone on a charging dock on my desk next to my monitor (audio bluetoothed to my stereo) and I can't help but think that the idea of the canvas should be expanded to tablets and the desktop app. I think its a nice surprise, even if its only a few seconds on a loop for the length of the song. I'm sure over time you'll add more to iconic songs of the past as you also keep adding them to newly released tracks.
I see there are plenty of other users out there that don't particularly care for the option. That's fine; it's not for everybody. I still think it should be expanded upon. When I'm using airplay at home to listen to music, it always gets my attention when the canvases pop up, but this doesn't happen when I have my iPad on airplay, just iPhone. The canvas seems like a more lively visual compared to just a plain 'Now Playing' screen. Just something to consider.