This could be quite interesting! Since the normal display usually takes most of the battery, thus as a person who reads a lot on my phone, having a more battery conserving and eye friendly option when reading could be really cool! But when I would need colour and full functionality I would still have the phone. The only real question now is the price, because I paid ~220€ for my phone, so if it costs equal or more, I don't think I could afford it - to basically buy another phone, but with less functionality...

I have been looking at E-Ink phones, which look quite interesting, would love to try one!