"It's not what you play, it's how you play it".
Sure, I like the idea, and I'm sure a lot of the Halo online multiplayer community do too, especially the ones that stuck by Halo 3 after the release of Halo Reach, but lets face it, Bungie aren't going to do this, they worked long and hard on Halo Reach, it's their newest game and has more players than any of their other creations, they stuck by Halo 3's multiplayer after it's release for a long time before Halo Reach was released, but now they're focusing more on Reach than 3, I also doubt that the whole community would move from the Halo Reach multiplayer to the Halo 3.