Hello Peter,
In the 21st century technology is no longer a constant; we can anticipate new ideas, new equipment, new software, new firmware, etc. etc., the list just goes on and on. I decided to make the transition to HD now since there is a window of opportunity to become really familiar with the equipment before everybody has a HD monitor to watch the clips on. In a couple of years most homes in North America will have 42" HD LCD displays in their living rooms and SD may be considered in the same vein as black and white when colour TV monitors became available.
As long as the camera manufacturers maintain the same footprint for updated models of their camera, the housing should be able to accomodate them so hopefully it will not be necessary to change the housing every time an updated version of a camera comes out. Eg. Amphibico's VH-2000 housing accomodates the SONY VX-2000, VX-2100 and the PD-150 and PD-170 cameras. The Phenom housing accomodates both the FX1 and Z1 cameras.
It requires a large outlay of cash to keep upgrading to the latest and greatest. However, if you wait until the perfect camera, and the perfect housing, and the perfect lights, and the perfect software, and the perfect hardware are all available at a reasonable price you will still be standing at the start line while everyone else is finishing the race. The footage that I have seen taken with the FX1 is amazing, and I anticipate equally stunning results with the Z1. Take the plunge, the water is fine once you get in.