One, until I hear otherwise, I am going to romanize Goukaiger, as Go-Kaiger. This is just based on the spelling of the katana, and it's likeness to Go-onger. That said, here are the latest rumors:
-The series will have definite influence from One Piece.
-Our heroes are humans from another dimension, who can use something like "Ki". The setup is described as Gingaman-poi (i.e. Gingaman-ish)
-Our main robot is composed of a "mothership" in the form of a Pirate Ship (forms the main body), with 4 animals forming the arms and legs respectively.
-One of the bad guys will probably wear an eye patch
-One of the bad guys has a hook on his right hand, in the fashion of Captain Hook
-Bandanas are worked into the helmet designs for the rangers