That's a shame cause that's the kind of port that would have given an advantage to the WiiU if it had been revealed before the launch. Now if we see it at E3, it will just confirm people how different the WiiU is from its next competitors...
Watch Dogs is bound to appear on E3 no matter what, really. I can see Nintendo at least trying to get Ubisoft onto their conference and tout exclusive features in an attempt to make theirs look like the "enhanced experience" though, without the post-launch malarkey that had Arkham City weigh down on Nintendo's last conference like a plague.
It'd look real good on Nintendo if they can strike a deal to have an exclusive reveal of it if they themselves want to do their best to paint a better picture for third parties.