E Ink's Sri Peruvemba says that there's generally a two-year cycle in E Ink technology as it takes some time to develop and test new generation displays. Sri says that we shouldn't expect a new monochrome E Ink display (to replace the Pearl) in 2011. I guess we'll have to wait till 2012!
What we are likely to see soon are speed improvements - full-motion video (24fps) using updated drivers and faster processors. Bookeen has already been showing about 10-15fps video on Pearl displays.