This looks interesting - I always wanted to use Paper for wireframes, sketches and mockups. This might come closer to that idea. However the biggest problem I still have with Paper is the fact that its canvas is always definitive and limited in dimension - even with the regional zoom option complex sketches will become crowded and busy. I'd love to have a close to infinite zoom out/in (especially out) option, thereby rendering the canvas practically borderless and as big as I want.