It reminds me of a feature I've always wanted, which would be a code unravel-er. Basically I'd like to be able to select a line anywhere in a codebase, and have said codebase expand to show me the entire execution path as if it were in one single scope, with the ability to re-collapse sections back into loops and functions while reading.
I think it would help to better understand the codepaths that can start to get fuzzy when jumping between abstractions. It would be great - not only for understanding unfamiliar code - but also for double-checking logic across longer code paths.
At any rate - great idea, great implementation, and beautiful website.