According to the WSJ, Apple is exploring the possibility of an iPad with a screen size “slightly less than 13-inches diagonally”. A larger iPhone makes sense given that Android devices are getting bigger and bigger, with Samsung generating healthy sales thanks to larger devices like the Galaxy S4 and Galaxy Note 2. Still, a 13-inch iPad would be a curious addition to Apple’s range of products, but not entirely without merit.
There are lots of people out there that use the iPad as their primary computer, and quite a few that use it for productive work too. A larger, 13-inch iPad makes sense if you imagine that Apple might want to position it as a MacBook replacement, for example. Retaining the 4:3 aspect ratio of the tablet could help to keep the size fairly manageable too. Having said that, Apple no doubt explores a lot of potential designs behind the scenes, so there’s no guarantee that a larger iPad would ever make it to market.