3D batteries will probably be replacing our current 2D batteries by next Fall. They will be 1/10th the size of present batteries and 20 times the time between recharge cycles.
Thus, we are now in the last stages of the 2D batteries and it is highly probable that Amazon will incorporate them in the next generation of Kindles. Obsolesence will be the big killers of our Kindles - not battery use.
Here is a link to the discussion of the new 3D batteries:
Also, color eInk screens are also right around the corner. The next generation of tablets may incorporate color eInk screens combined with 3D batteries.
How many folks today still read eBooks on their Kindle 1? My old Sony PRS 505 was so obsolete that no one would accept it even as a gift. I was forced to donate it to the nearest public library who may have even discarded it when I left.