Is 64GB just not cutting it for you? Personally, I've always been fine with an 8GB or 16GB (my current iPhone 4 is a 16), but some people may want a bit more, especially if they keep a lot of movies on their iDevice or record video with it. If you're one of those people, you may be interested in this tweet from iOS hacker iH8sn0w. The tweet pointed out an addition in the iOS 6.1 beta 5 BuildManifest.plist, indicating partition sizes for up to 128GB.

The inclusion of this in the BuildManifest doesn't make it a certainty that Apple will release an iDevice with 128GB of storage, but it does make it a possibility.

As seen in these screenshots a writer at iDownloadBlog took, the iOS 6.0 .plist did not contain an entry for 128GB, while the 6.1 .plist does:

iOS 6.1:

iOS 6.0:

The field labeled SystemPartitionPadding indicates that there is, at the least, heavy consideration of including 128GB in the iDevice lineup. Or, maybe this indicates an iPod classic-esque iOS device (I doubt it, but I can wish).

Thanks to iDownloadBlog for providing the images and the information.