Maybe if it was old Green Day and Offspring it would be awesome. But not how Green Day is now. I'm not a fan of their new stuff.
Both of them are great bands, and they both acknowledge each other's respective roles in bringing punk to the mainstream in the 90s. First it was Green Day with Dookie, then the Offspring with Smash.
Though other than that, I really don't know what the bands think of each other. Last I've heard, The Offspring respected Green Day's music, but I've never heard Green Day really talk about what they think of The Offspring.
Personally, these are two of my favorite bands, Green Day being my favorite band of all time. They can both put on outstanding concerts; age is not even a factor for them. It'd be out of this world to see, but I doubt it'd happen.
Some here are missing the point. GD and Offspring not only share the punk roots but also the fact they are the most popular punk-rock bands (After American Idiot GD literally conquered the Solar System, it's clearly more popular than Offspring), both have taken chances in music at the expense of being labeled as sell-outs. And thank God they don't have the same style as it'd be pretty boring to see two samey bands. That said, I can see each band cover one another and that going really well. PS: if some don't like my threads don't post then. I thought it'd be cool to discuss The Offspring and shake things up a bit in this ghost town of a forum.
I, personally, would not mind seeing a tour with both bands, but I don't know how much of an overlap there is between their fan bases these days. Could be like the Charlotte Weenie Roast last summer, where a good chunk of people left right before the Offspring played, because they were there to see a different band.