We have seen customizable keyboards before, the latest craze were keys that had OLED displays that would change according to which application or game you were playing. The big thing with this was that the OLED keyboard were and still are extremely expensive, making them more of a luxury item. There are even companies that sell keyboard covers and caps that have shortcuts on them for people who use the same programs all of the time like Photoshop and Premier Pro.
Sonder Design has recently announced their Sonder Keyboard. It is designed to look like the typical Mac aluminum keyboard, but 50 of its 78 keys are fully customizable.
Each of these 50 keys have an E-Ink screen that allows you to full customize each key. So you could easily display shortcuts for the program or game you are in, application launch shortcuts, and so much more. Here are their examples for Photoshop and Half-Life.
Sonder Design is currently offering a Mac version for pre-order at a price of $199 and that price will go up to $299 when the keyboard is released. They also mentioned they are working on a Windows version. There are also talks about doing a Kickstarter campaign to fully fund the project. Check out their website for more information.