Hybrid Fat/Snow Bike I've seen some bikes with a pugsley or similar fork and 3"+ tires on a hard tail mtb frame.

-Has anyone done this them selves? 
-Do you really notice any flotation with only one fat tire and one regular? (2.3" is the max my rear triangle will accept)
You're describing a Fat-Front setup.

Cornering on soft surfaces should be improved, as well as shock absorption if you run low pressure, but drive would only improve in the case where the fat front tyre can compact snow enough for the regular rear tyre to dig in less than it would on a standard MTB.