The font of all reliable tech news Digitimes reported on Friday that E-ink is currently developing a 40" to 5-" E-ink panel, which they plan to release this year:
E Ink Holdings (EIH) has offered e-paper displays up to 32-inch and is currently developing even larger products, with some set to be released in 2016, according to company chairman Frank Ko. However, as the company pushes the envelope in terms of developing larger products, it may need to find manufacturing partners in Taiwan.
EIH only has a 2.5G factory, which has insufficient production capacity and is not suitable for economical production of large-size displays, in the 40- to 50-inch range, Ko said. Therefore, in the future EIH may partner with panel makers AU Optronics, Innolux and Chunghwa Picture Tubes, Ko indicated.
No clue who is going to use it, or why they would want to.
About 18 months ago E-ink announced a 32" panel, one which was developed specifically for signage. That display had a screen resolution 2560 x 1440 (grayscale) or 1280 x 720 (color), but I'm not sure anyone is actually using it.
Lots of retailers are replacing their static signs with digital signage, yes, but all of the ones I have seen were either LCD or OLED, and not E-ink. Walmart, for example, has retrofitted their stores with LCD signage, and both AMC theaters and Poppy's have replaced their signs with huge Samsung signage units (available in six sizes ranging from 32" to 75").
E-ink certainly had the right idea to get into signage, but from what I can tell they are being out-competed by a product that has a faster refresh, better color quality, and (probably) a lower price tag.
So while E-ink is developing a 40" screen panel, I can't tell you who would actually use it.