Hmm, if I remember correctly, I once saw a thread with a huge load of house specific bases which looked so damn awesome and maybe there were jump gates as well, I am not sure but anyways. The current model fits into Liberty quite well, in my opinion, I lack the imagination for a jump gate for Liberty right now. For Rheinland, I would take something in its dark green shade with a bulky heavy and menacing look, a bit like the Gallia gate, it shouldn't have many roundings but more like an ALG mover from the front.
Kusari could have a jump gate that fits the look of their battleship color, a bit more light and a few neat cutting edges like the Tokugawa has on its top around the gate, but it is very easy to overdo something in this case.
Bretonia is also not so easy for me to imagine but definitely the dark color shade of the bretonian capital ships, that would be possible and maybe a "skin" that looks similar to the armor on bretonian warships.
EDIT: I agree with the above people though, it would be a lot of work so I would focus on more important issues and see it as a possibility, I would rather see a new model of the Raijin :3