Like that, yes - but there are differences. The keyboard could be completely standard display technology. (However you might use a lower resolution display for the keyboard as compared with the actual display.) Standard could mean cheaper. eInk displays today are fairly expensive.
eInk has low power consumption but is slow to refresh. Refresh speed might be an issue if you want “Shift” to result in a dynamic change to all “keycaps” (as happens with some on-screen keyboards).
eInk doesn’t do color very well.
I have my doubts too - but we’re brainstorming, right? So just throwing ideas into the mix.
(I just copied those two ideas from my previous post on the exact same subject.)