Well, I don't think they're likely to come out with something to make be go for a replacement, the Sony Reader is too well suited to my needs.
However, if someone came out with an A4 e-ink device that allowed viewing and annotating PDF files (and able to merge the annotations back into a PDF file), and had a battery life of somewhere in excess of 20 hours (absolute minimum) between charges, I think my wife would likely be interested for paper-grading purposes. Oh yeah, the price would probably have to be under $500.