By my part, I wouldn't buy another 6" ereader like the ones currently sold, because
1) what an eco-savvy choice would it be, if we buy a new one before my old one stops working?
2) currently sold ereaders are a too weak improvement over my 2011 device
3) the big amoled display of my smartphone works very fine for reading, with its low light emission with black background (much better than any LCD, Retinas included). So it almost completely replaced my e-ink, for evening and bus/underground readings
Edit: the following picture shows my setting for reading in complete darkness and