One little funny thing that's been on my mind is redoing the canvas system for the new engine, which is not really the best... The current one is basically an immediate draw, meaning.. no state can be held... you just, draw draw draw draw, but this is contradictory to the fact that all game objects in a typical game session have retained state anyway (how do you think collision works??), thus allowing them to retain their existence a little more consistently.
I'm not exactly aiming to create a scene graph however, and I don't really want nesting or anything fancy (doesn't make much sense), though it would also be nice if you could move layers and the relative content within them move as well... apply effects, so... a scene graph, kinda.. :) Perhaps a nested approach could be separate from the drawing context in general, though, and just be a literal thing that's handled externally.
Anyhow, I cooked up a (very lazy) image showing how it'd work.