I can generate and display an airspeed based on the ground speed from GPS and the previous windspeed and direction. In most cases this will be near enough to provide the pilot with sufficient useful information. Add the pilot selecting the appropriate 'pitch and power' for cruise to that and in most instances the information is sufficient to recover the aircraft.
You are assuming 2 things; that SatNav gives horizontal speed and ignores vertical speed components and that SatNav is unaffected by environmental aspects such as electrical weather systems. Existing Integrated INS gyros do all this successfully in vehicles such as submarines to space craft.