Next generation iPad cases have already begun popping up in China. The latest comes from the case manufacturer Chinee, who claims Apple will release a slightly thicker iPad, possibly called the iPad 2S, sometime this year.
Case manufacturers have already led us astray with the iPhone 5, and now they're starting to contradict each other when it comes to the next generation iPad. An unnamed iPad case designer recently told Cult of Mac that the iPad 3 would be thinner, not thicker. However, Chinee claims to have inside information from sources within Apple’s supply chain. If Chinee is correct, the new iPad will be 1mm thicker than the iPad 2.
Case manufacturers have been good sources of information regarding future Apple designs in the past, but lately they seem to be jumping the gun based on internet rumors. I would take any premature iPad case designs with a grain of salt until Apple makes an official announcement.