Every time this topic comes up, I think, "the kindle is perfect as it is!"
Well, not quite true . . . I can always think of tiny tweaks that would make it more perfect for me.
They ALWAYS come up with something more . . . sometimes something I (or others here) have thought of and sometimes all new stuff.
Example: I thought the PW was fantastic . . . the second iteration tweaked a few things and was better. THEN, the Voyage tweaked a few more; specifically the adjustable lighting, page turning on the bezel, the weight and shape, and improved placement of the power button. And its release was more or less coincident with the fixing of the cloud collection functionality.
At this point, I can honestly say the ONLY thing I would really want that isn't already part of the Voyage is a single button on the device that takes you HOME in one step.
Others here have said they'd like to have the ability to listen to books back . . . . .
To answer the question posed: I don't know.
Here's the Kindle release schedule since it's inception:
Nov 2007
Feb 2009
Summer 2009 -- the DX model
Aug 2010
Sept 2011 -- both Touch and new Basic model
October 2012 PW
Sept 2013 PW2
Sept 2014 Voyage -- as well as new Basic model with touch screen. (They no longer sell an eReader without a touch screen.)
The Fire tablets were first released in fall of 2011 and there has been at least one new model each year since.