Eink readers will limp on with tiny improvements until another display tech like liquivista comes along to supersede it. I think there will be a demand for a device with reflective display for a long time because of the eye fatigue factor. It may not be a dedicated reader, it may have tablet functions the way the iPod touch is like an iPhone that does not make calls. Also, since I don't expect Amazon to get out of the book business any time in the foreseeable future, they at least will want to make dedicated e-readers to cater to, um, dedicated readers.
In short, there's no need to hoard eink readers
But yeah, it's interesting that e-reader prices haven't dropped way more. Moore law doesn't apply to display but what about economy of scale?