1.5" appears to be between Full frame and APS-H (1.3x crop)
1D4 = 33.5 millimeters = 1.3 inch
1DX = 43.3 millimeters = 1.7 inch
G1X = 38.1 millimeters = 1.5 inch
Although that is how it might appear at first glance, the inch system for sensor size is not directly translated to diagonal length.
For example, a 1/2" sensor is 8.00mm diagonally, a 1" sensor is 16.00mm diagonally (just a hair bigger than Nikon's CX sensors on the Nikon 1 series).
The 38mm you have up there refers to the outer diameter of the image tube that would have been used in television cameras of the old.
Following the proper conversion, which is roughly multiplying the inch measurement by 2/3 (not exactly), you get a sensor that is 24mm diagonally.
Interestingly, the Canon APS-C is 2-3mm bigger diagonally that this supposed 1.5" sensor, which is odd, since Canon could cut research and development, and production line costs and just stick a APS-C sensor inside their new compact ... though, either way, the lens would have to be gigantic (by compact standards) to satisfy the rumoured zoom.