from what i read the 128GB model was requested by companies as a condition of them buying ipads for corporate use. lots of files like blueprints use a lot of storage and no one wants to pay the carrier fees to download from the cloud
Correct me if I'm wrong, but here is a little history lesson that may or may not prove relevant:
I think the only time Apple has ever upgraded storage for an iOS device part-way through the upgrade cycle was the original iPhone and the iPad 4. The original iPhone came in 4/8GB sizes. On February 5, 2008 the original iPhone was upgraded to a new 16GB capacity option. Later that same year, they came out with the iPhone 3g that only came in 8/16GB sizesdropping the 4GB model altogether in favor of the larger capacity offering.
Now this year we have the iPad 4 get a 128GB capacity on January 29th. That's FOUR models of iPads, across multiple versions for WIFI and various cellular radios. To add further complexity, the iPad 5 is expected to come in Gold, Silver and Space Gray. So that's an additional color option. Given the precedent of the original iPhone and Tim Cook's penchant for keeping a tight supply chain I wouldn't be surprised at all to see a 32/64/128GB lineup. Not to mention that competition is finally starting to heat up a little bit.
But perhaps that is just wishful thinking since I'm getting a 128GB no matter how much the darn thing costs! My 32GB iPad 2 is always running low on space.