Apple's primary motivation, if The Guardian's "industry sources" are to be believed, is to offer full size iPads with 4G connectivity that are compatible with the U.K.'s Everything Everywhere network. You can also expect Apple to take the opportunity to update the proprietary dock connector that's been a mainstay of iDevices for quite some time, replacing it with the new 8-pin Lightning connector that was introduced with the iPhone 5.
The sky's the limit on what else Apple decides to upgrade. While not a complete revamp, Apple may choose to inject its 9.7-inch iPad line with a faster processor, especially as Apple attempts to sever ties with Samsung in the manufacturing channel. A higher quality display and bigger battery are both in the mix, as well. The goal would be to create enough separation between the iPad Mini and regular iPad, and also to ensure that its higher end device is capable of maintaining its lead in the marketplace.