According to the new Pixel Qi products page at http://pixelqi.com/products, the 7" version of the Pixel Qi screen, thus suitable for more portable tablet form factors and e-readers, may be on display and perhaps available as samples starting this January at the CES trade show.
7" samples for CES 2011 possible
And according to their September 17th blog post:
New Screen Development: 7″
We are developing a 7” screen for tablets and ereaders that is planned for mass production in H1 2011. Samples will be available earlier, perhaps by late Q4 2010.
As I am typing this post on my awesome 7" Archos 70 Internet Tablet, I can imagine how it would be to have the device be even lighter (than its current 300 grams, vs 380 grams Galaxy Tab and 680 grams iPad) with a smaller battery or to have it last upwards 50 hours with a reflective screen suitable for e-reading. Kindle 4 should definitely use this, and this is I think the reason for Amazon to be secretly preparing their alternative Android application store.