We received one of the new model of Time Capsule and took it apart. You can see the pictures in this article. Unfortunately, there is nothing new except the increased storage capacity.
Another thing is strange. On its website, Apple advertises on the fact that the hard drive inside is a "server grade" hard drive. However, the disk that we found inside is a simple Caviar Green with 64 MB of cache. It means that we had "server grade" disks in the Time Capsules we upgraded with a similar disk.
[Update] According to Western Digital, this disk is a general public model. There are also similar models for servers, but they are more expensive as they have a lower bit error rate 1x1015 while this one has 1x1014, 600,000 load/unload cycles (300,000 for this one) and is covered by a 5 years warranty, while this one is covered for 3 years.
Apple is using the fact that "server grade" is not an official reference, it is a little like phone carriers did with so called unlimited 3G data plans.