This keeps coming back up on #jollamobile. Nokia have already used an LPS on a non-AMOLED screen. It's not as bright, and I haven't seen a comparison of power consumption, but it does work. However, this doesn't mean that Jolla will be using this (I can't find a quote, but I'm pretty sure their Twitter said they weren't at one point). It does mean, though, that if developers have enough HW access to the Jolla device, such a feature could be added.