In fairness the most recent rumors of a refresh point to a July release date. Were that the case there would be very little opportunity outside of Google for any kind of hardware leak particularly if mass production has yet to begin. However that in itself makes me skeptical that a refreshed N7 would make an appearance at I/O. Announcing a product 2 months before release makes it difficult to create an ongoing sense of momentum and excitement in the time period between announce and launch, particularly when WWDC and potential new iPad hardware may be announced, or launched during that window. Guess we'll see soon enough.