My thoughts about what apple might be up to. We assume, it's a tablet, or at least somthing flat with a big touch screen. The iPhone is about 4.5 x 2.5 inches, let's assume it's something at least three times the size, 4.5 x 7.5 inches. That's not very big but big enough to see something and small enough to carry it. As it is a device which by it's very purpose should be held in one hand, it must not weight much more than 300 grams. The iPhone weights about 150 grams. Three times this weight and by optimizing the space and weight, the tablet could actually weight just 300 grams. Thats what the physical goals are.
What can you fit inside such a box? The screen, CPU, GPU, RAM, Flashmemory, Notworking, Huge Battery. As Apple tends to go wireless, there are possibly very few connectors, like for example for headphones and of course a docking connector.
What can you expect to be on the device? Huge computing power is not possible, so aside from browsing and using little apps, there is not much possibility. But maybe this device just acts as a remote, reducing the computing power to just display content and the actual performance tasks are done on a remote computer. The pixelcount is small enough to stream lossless (or almost lossless) to the device or maybe, there even is the possibility that the device just receives cocoa messages and displays the contents accordingly. If so, the computing power of the device could be reduced drastically which allows to make it very thin (less heat issues).
Where could this device be used? Anywhere where a person just needs to do a quick task and exchanging data with a server, for example when doing inventory, postmen signing mails, doctors checking patients, ... There sure is a market for that, the existing devices just are not appropriate enough.
Just my thoughts, Would be nice, IF there will actually be something.