Not possible. The control layout and other significant features changed significantly between different models, as did lenses - M1/M2 have a 28-100mm equivalent, M3/M4/M5 have a 24-70mm equivalent, and M6/M7 have a 24-200mm equivalent, this latter lens requiring interchangeable ports in order to house. There are a couple models (Sony's own, plus SeaFrogs/Meikon) that support M1 through M5, and a SeaFrogs model that supports M3 through M7, but if you upgrade your RX100M2/Nauticam setup to a new camera, you will absolutely need a new housing.
As for differences - it's still a 1"/20MP sensor, but the newer models feature
much better autofocus capability (M5 and up bring phase-detection autofocus, whereas earlier models are contrast-detection only) along with better burst capabilities, although this latter feature is largely useless underwater, especially if you shoot with strobes. The 24-200mm lens on M6 and M7 is capable of extreme macro with close-up lenses (see
Jim Decker's review for samples), but is difficult to use and requires different ports for macro and wide. It can be argued that the 28-100mm lens on the original RX100 and M2 is the most versatile for underwater use - the 28mm wide end is perfect for wet wide lenses, and the 100mm long end is better for macro than the 70mm found on M3/M4/M5, while still functioning with a fixed port.