I had a very similar idea to this when the apple patent came out for the organic light emitting plastics thing, though using oled displays makes more sense as it's much more commercial product these days (plus we don't really know what kind of quality display the apple tech would get for dispalying letters and icons).
I think if apple bought this idea and took it on, they could improve it in a number of ways. First the keys look pretty awful. They look too square, flat and uncomfortable to type on. Secondly, using these (
http://www.engadget.com/entry/1234000410050327/) oled displays, they could use no power for displaying the images, until they have to change, which will improve battery life by a fair amount. Next, with their universal remote control patent, they'd have the base for being able to send the images to each key on the keyboard. Either that or have it so the OS automatically checks what shortcuts the system and current app have set and map them to they keyboard, and change them when modifiers are pressed. Finally that app launcher could become a touch sensitive strip, similar to the iPod's scroll wheel, but using oled. Then it could become a kind of hardware dock. It could mirror the dock or display and app you wish using preferences. This way you could set the icons to any size and have the dock hidden on the screen while still being able to see the app icons on your keyboard, including any status parts of the icons, such as unread mail etc.
I'm not sure how big a market there would be for this though. If it was realistically priced then creative professionals would probably buy it as an upgrade or replacement. heavy iLife users may buy it too, and people that just want to have a cool looking keyboard, as well as people that use multiple languages or layouts (it's annoying trying to find all the accented characters unless you know them off by heart). It could be another product they push out to windows users, just like how the iPod became available and the screens went DVI. Selling standard peripherals to both mac and pc users could be a new direction to make money, along with a multi button mouse. Generally apple couldn't really sell a keyboard to windows users cause of the different keys, but with this they could, and target it to people that buy a mac as a second computer, so they could use the keyboard for both (as well as duel boot mac/windows computers). Generally though I don't think it would be a big seller for windows, as a keyboard doesn't have a must have quality like the iPod does. People don't really replace their keyboards unless they are in niche markets like geeks, power users and gamers. It would be great for gamers, but I don't think Apple is the first company a gamer would look to when looking for hardware. It could become a nice little lust item for the cool kids though, especially if it docks with the iPod in some way, and is compatible with any future home media device (could be useful for things like web tv and managing your content)