There are many many products that do this. They're all crazy expensive though and they generally use LCD tablets.

The ones we've had at the last two companies I've worked at were battery powered and lasted for a day - somebody has to go around and swap them over once per day.

I agree an e-ink solution would be much better but then these companies would have to do their own hardware since nobody sells e-ink tablets with a proper OS and they're way too niche to do that.