As I've mentioned before, Sugar isn't built on the GNOME desktop, but it is built out of the same components (GTK+, DBus, etc.), so the big crisis in direction GNOME & GTK are having right now will have a serious impact in the long term architecture of Sugar. Chris Blizzard (formerly of OLPC) has a good analysis and you can trace links backwards if you want more background.
...I think that GNOME has evolved into two different projects, each struggling to share code and be successful. One is the “classic desktop” as we used to call it at Red Hat and the second project is built around servicing the mobile and highly-specialized desktop experience market. These are not the same thing, not by any stretch. Different audiences, different goals, different players and different revenue models. As a result you can feel some measure of friendly, but sometimes misunderstood confusion in the GNOME project because the underlying change isn’t fully understood. [...]
...That’s also why I’m calling this a duality. Two projects existing as one. One without a great deal of success, but an end-user identity and brand and goals, and another with a chance to succeed but without much identity or end-user goals. It’s going to be a rough ride and I think that in order to find success we have to find a way to merge the two into a single set of goals. The desktop isn’t going anywhere, but the mobile project isn’t going to produce GNOME-visible results either. GNOME will be well-hidden behind someone else’s branding and experience. And maybe that’s fine, but it’s not the way to lead and win in the end.
Anyhow, read the whole thing if you want to peek into the baroque politics of advanced open source projects.
Ideally, strong development on the "mobile" thread will be good for inexpensive computing for students, including a more robust back end for Sugar.