Well E-ink and Epson have
announced a 300 dpi screen (current displays are about 160 dpi). It's for a 9.7" display right now.
A resolution bump is the most important thing to me for next generation e-readers. I hope the next Kindle uses it. But I assume it wouldn't be ready for this year and with Amazon launching their tablet sometime this year I imagine a spring 2012 release for the next Kindle seems likely. But I'd love them to surprise us.