My own mindless speculation, that is.
Remember this Branch thread from earlier in the year, wherein a bunch of Apple-focused pundits posted some of the tips and whispers they’d heard?
I’ve heard from several sources that there was/is an event planned for April, new 9.7 inch iPad if it’s ready.
If we don’t see [a new iPad] in April, I’d guess that it’s late. And if it’s late, I think they’d do a standalone event in May rather than hold it until WWDC in (I presume) June.
I don’t think they would want to unveil the new iPad at WWDC alongside iOS 7, because the new iPad won’t ship with iOS 7.
Redesigning iOS in seven months has been a tall order, and the iPhone-only demonstrations and betas are clear evidence of that. There are only two places where mockups of an iPad running iOS 7 have been shown: in the compatibility chart, and on the iTunes Radio page. Since iPad apps have their own user interface philosophy, components, and styles, it’s reasonable to assume that these are still in progress.
Furthermore, since well-connected pundits heard that an iPad refresh was scheduled for spring, yet it did not occur, it’s reasonable to assume that Apple is still working on it and trying to shoehorn a launch in for later this summer or in the fall. Therefore, it’s reasonable to guess that an iPad event later this summer could also be the first real glimpse into iOS 7 on the iPad.
Update: iPads are also the only non-retina devices supported by iOS 7, and the new user interface — with its use of lighter font weights and thinner graphics — is very much retina-favoured.