There is no way the Bionic will be an improvement over the Atrix in turn of opening/running multiple apps. It's only got 512MB of Ram, why have all the trouble of a Tegra 2 w/o the RAM to support it?
Motorola once said in CES that the Atrix will be available in Verzion late Q4
Maybe they changed their mind , especially that the leaked Droid X 2 looks allot like Atrix 4G (Spec wise)