LaCie showcased their 2big Thunderbolt drive at CES 2012 and it has now started shipping. 

The LaCie 2big Thunderbolt Series is essentially the LaCie Little Big Disk in 3.5" form factor. It has two swappable 3.5" drives whereas the Little Big Disk has two 2.5" drives. 3.5" drives offer larger capacities and better performance, particularly with hard drive. The 2big is rated at transfer speeds up to 327MB/s while the Little Big Disk tops out at 190MB/s (both results are for the non-SSD versions). LaCie has an 8TB model on their site as well but there is no price listed, which suggests that it's not shipping yet.

There are also two Thunderbolt ports for daisy-chaining, so you can daisy-chain several 2bigs or other Thunderbolt devices. The 2big most likely uses the same SATA controller as the Little Big Disk, which means you are limited to two SATA 3Gb/s ports. For the standard configuration this isn't an issue, but people who are interested in swapping the hard drives for SSDs should be aware that the SATA controller will be a potential bottleneck with the fastest SATA 6Gb/s SSDs.