Current fingerprint data is stored in a separate location within the phone itself. Where would the data be stored in the keyboard? I don't see the purpose of using the fingerprint to unlock a computer.
Shouldn't be too hard to implement but location could be an issue. I doubt Johnny Ive wants to add a sensor next to the keyboard. Would require some additional circuitry on the logic board to store the biometric data separate from normal processing.
Lots of other laptops have had fingerprint sensors but the integration with Windows and other apps was lacking.