Ultrapeers are a little different from Fasttrack-Supernodes. The latter actually cache the files clients are sharing and shield their leaves completely from Queries. Ultrapeers do shield their leaves from a portion of the traffic, but not from all of it. You also can connect to more than one Ultrapeer at a time, which you can't do with Fasttrack.

Btw. it's been nearly a year since I read the first articles about Gnutella-Supernodes and whether or not to implement them. Some articles were argueing Gnutella would not remain pure if they implemented any kind of hierarchical structure. That was a couple of months time before I ever heard of fasttrack - I was still using Napster, then. - This is just to illustrate what 'soon' can mean, if you're talking gnutella. And I don't see the GDF trying to speed things up. - But that's just my impression.