kkfok,
I looked at the plastic housing and it does seem to be advertised at about four pounds for the unit.
The Gates is quoted at 11.3 pounds with camera, camera battery and wide angle port, which leads me to believe the difference is less than seven pounds. If the camera plus battery is about 1-1/2 pounds and the port is 2 pounds (just guesses) the real difference becomes more like four pounds. I don't know anything about the plastic housing - I presently use an Ikelite plastic housing and don't care for it. The buoyancy was a problem which took me months to overcome. The light weight decreases stability underwater adding to camera movement when I don't want it. The front/rear balance isn't too good. The camera "bobs" up and down if I use a control. Other than that, it's OK 
So for stability, complete access to controls and Gates reputation for solidity, I'll take the added four pounds. It's still light enough to take as a carry on for international flights.
My two cents!
Tom
PS: Still don't have a clue about when the camera will be available, nor about any possible competing products!