Out here in Calif. they are talking it up. Many say that the reunion will more likely be a one-off. But sources say this gig is not a one-off and the band has other shows already planned. I'm sure that de la Rocha is stoked, they say he has already shut down his solo career, website and all.

As far as Cornell vs. de la Rocha with vocals, I don't think Cornell could pull off the flow of intensity RATM creates when they're in sync together. They feed off each other.
Just as I think that Cornell's magic was in Soundgarden, being in sync with his food chain.
If someone reading this post happens to become fortunate enough to create magic with another musician(s) and form a band that generates your chemistry as it spreads like wildfire, Do yourself a big favor and practice being neutral, just go with the flow.
So many Band members have dissolved their magical wit through pride, greed and egos when trying to prove they made the band alone.
Look at Axl Rose, I don't care what band he joins or forms, It will never be close to the chemistry that inspired GnR. Neither will Slash for that matter.
Think of all the others that threw their magic away and never got it back again.
Zach de la Rocha has nowhere else to go. Hopefully they can ignite the chemistry again.