You can't get one yet, but in the future, you might have the option of adding a keyboard with e-ink display to a Surface tablet.
Microsoft Research is working on just that, sharing a video look at the early prototype of what it calls a DisplayCover. Patently Apple (of all places) noticed the video on Microsoft's MSAppliedSciences YouTube channel.
Why add a secondary display to a keyboard?
For one thing, you can gain back traditional screen real-estate by moving menus and other options to the e-ink display, as shown in the video.
E-ink also uses very little energy, just requiring power for changing images or text, so this type of keyboard won't need a very large integrated battery.
Depending on the implementation, it could sip from the tablet's own battery, in which case, the impact to overall run-time would be minimal.
For now, you can clearly see this is a true prototype rather than a finished product.
The ribbon cables that attach to the keyboard, for example are one big clue. And the keyboard is far thicker than Microsoft's currently available Surface Touch Covers and Type Covers.
If Microsoft can slim this down and add an e-ink touch display to its tablet keyboards, however, it could have a new accessory option for its Surface line of slates.
And it could even sell a more generic Bluetooth version to work with any other Windows 10 tablet, although I'd rather see the company keep its best hardware products exclusive to the Surface brand.