Limited Edition Modern Warfare 2 Xbox 360 bundle, we had a chance to grill Microsoft's Albert Penello, director of platform marketing for Xbox, about the bundle. While Pinello confirmed the bundle's absence of any additional accessories – no high-definition cables, no WiFi adapter – he also commented on the 250GB hard drive. When asked if Microsoft had any plans to sell the significantly embiggened hard drive separately, Pinello said, "I wouldn't say plans. Maybe. I hear this story every two years. It was the 20s, and then the 60s, and then the 120s." Not that you could afford it anyway.
So, Microsoft doesn't have "plans" per se, but Pinello pointed out that, historically, these things become available separately. Until then, if you want a massive 250GB of Xbox storage, your only avenue is purchasing the $399 Modern Warfare 2 bundle.