Currently I have a handful of the all-in-on seeed studio reTerminal E1001's that rotate book quotes I've highlighted on my kindle (jailbroken, KOReader+BookOrbit) once a day so they can last months on a battery charge. But with BTLE you can go years on a single charge, update more often, and push to the device to force an update (all things not possible when deep-sleeping wifi for 23.99 hours out of the day).
e-ink displays are so nice and once I get the BTLE+OpenDisplay setup perfected I'll probably grab ~10 more boards/displays for other places around the house.