I have a bad feeling this won't make it in on time for WP 3.9. Nacin posted it needs a lot of work with some UI polishing, but right now support for wider-than-default widget controls hasn't landed yet and I don't think that's a particularly easy nut to crack (if it was, it would have made it in months ago).

Anyhow, this is some amazing work by Weston, Shaun and others. It's gonna make a lot of people super happy.