Actually I don't think that's necessary - I'd much rather they focus on making individual loads very fast, instead of pre-loading data. 9 times of out 10, I'm not going to peruse the ENTIRE directory structure even one level deep, so it should only get the data I want.
Also, they would need to store that, and I don't necessarily want my browser storing my entire directory structure (and possibly file contents) for any amount of time other than when I'm actually browsing it.
Try it out, it really is very fast without having to eagerly load anything at all.