I think it's possible we'll see it at WWDC but not very likely. But if apple does do this I think it would really only be on sale for developers for a while. The only reason apple would have a reason to unveil it early is so developers can optimize their apps. But that would take horrible summer iPhone sales to nothing. So it's really going to be interesting to see how this all works out.
I think that this year the rumors about a larger iPhone coming in September will get big and mainstream enough that it will kill the current iPhone sales anyway. Tim Cook even admitted that last summer sales of the 5 were affected by rumors of the 5S.
Apple could announce the resolution of the iPhone 6 at WWDC, let the iOS simulator support it but offer no other detail (no picture). This kind of news probably wouldn't rise much above the rumor noise.