The shipping delays seem to suggest an update soon.
I could see 12.9inch updated to feature parity with 9.7inch (gaining True Tone display and better cameras on the front and back) without an event, like the new iPad updates.
Then the new premium bezel-less iPad later (October?) so as not to spoil the bezel-free form factor reveal for next iPhone. That one will probably be 10.5inch or so on the diagonal, with a higher resolution.
Either way I'm holding off for now as while I do want to invest in one, I'm not made of money and I'd be annoyed if I got one now and it was updated at any point this year. I'm also really stuck about the sizes still!