Many people were slightly disappointed when the 4K Fire TV came in the form of a lower cost dongle with no ethernet (though it is a great device). Many AV enthusiasts wanted a more powerful box and we have continued to hope this would be released.
There were leaks last year that Amazon was releasing 2 new Fire TVs, so the launch of the dongle was even more disappointing.
It now appears that the leak may not have been that inaccurate after all and the 2nd device is for 2018 and may finally have a decent successor to the original 4K Fire TV. FTVNews has discovered a page on Amazon's website where you can sign up to receive more info about the “Fire TV Cube.”
The original leaks from last year showed a cube design that looks like a hybrid between the Echo Dot and a Fire TV. With Amazons sign up a page using the term Fire TV Cube, we can assume those leaks were accurate, and a hybrid device makes a lot of sense.
Sadly we don’t know anything about its specification, but you can assume it will be at least as powerful as the current 4K model offering HDR10 and I would expect this would get bumped up to HDR10+ which is the format Amazon have adopted. It will be interesting to see if the new model offers Dolby Vision.