It is interesting the different approaches Amazon and Kobo are taking.
Amazon has 3 300ppi 6" devices, Kobo has none.
Amazon's cheapest 300dpi device is $119. The closest Kobo comes is 212dpi for the same price.
Kobo has bigger devices.
I would guess that a Kobo 6" 300dpi with haptic buttons and Comfort Light Pro would be a Kindle Killer.