I came across this patent application 20120008928 for an universal underwater camera housing. Most of the current models from companies like Amphibico, Nauticam and Ikelite are very expensive and made for just a specific camera model - once you upgrade it, you will also need to buy a new housing. From the patent application:
"A universal underwater enclosure has a spherical shell having a hollow in which a camera, camcorder, or other device can be inserted, a lens attached to the shell that can be opened to insert a device, and glove assemblies extending into the hollow for manipulation of a device placed therein. The glove assemblies have fingers and not full gloves, reducing the dimensions of the enclosure—thereby minimizing buoyancy. A mounting system attaches to a device's tripod mount receptor, fixes the device, and allows it to be adjusted in three dimensions. A pressure equalization system relieves stress on the enclosure, which exhibits neutral buoyancy. A flash mounted on the shell operates independently of any device. Modular lens pods replace the lens to accommodate various other lenses. The glove assemblies have perimeter lips secured to the shell by fasteners and a bezel around teardrop-shaped cut-out holes in the shell. The fingers allow access to all of a device's controls."