Here's my take:
First, I just want to request the guys deciding the engine to put anything BUT a 6.2 in it, but make it better than the LS3, just so we can see 2010's head explode.
Secondly, I think this entire name thing needs to be taken with a grain of salt.
The DI 3.6 gets 304 hp in the Caddy, 283 in the Chevy Traverse. An even 300 in the Camaro? That makes perfect sense. The tunes are all different, but essentially the same engine. Based on the spy pics showing a V6 with the Caddy DI specific engine cover, plus Ed's comments here, I am 99.999999999% positive we'll see a DI V6 model making somewhere in the near neighborhood of 300 hp. Enough to tackle the 350Z (though short of the upcoming 370Z) Hyundai Genesis, and current Mustang GT (though again, upgraded soon). So really, the V6 is going to be a legit performance car, not just a style-mobile. Sweet.
The LS3 makes 430 hp in the Vette, 402 hp (expected) in the G8 GXP. Perhaps, as Scott suggested, Ed misspoke and meant 6.2, meaning possibly a detuned LS3.
OR...
The L76 in the Pontiac G8 application makes 360 hp, but it has been said that with just premium gas and a tune, we're looking at 400 hp. So I don't think a 400 hp L76 variant is out of the question.
Or it could be another Gen IV combination, which, despite sharing common names, all of these engine variants are just Gen IV combos. A lot of parts can be shared and swapped.
OR...
Maybe they can get a Gen V out that quickly. And then we just forget, as usual, everything we think we know.
Still...in the end...400 hp, with fuel saving technology? That's a good thing. And though 2010 will disagree with me, it doesn't make much difference whether that's done with 6.0 or 6.2 liters.