Would a wireless fly by wire system be practical?
The fly-by-wire is absolutely vital for control of the aircraft, and the three dominating factors here are safety, safety and safety. Weight is not one of them. The fly-by-wire system is triple or quad redundant: instead of removing a set of cables, the manufacturers are installing 3 more cable looms, just to make sure that the system always works.



Wires are safer than wireless!. There are active transmitters and receivers in wireless systems, which can fail. Signal reception depends on the quality of the space between transmitter &amp; receiver: can the signal always penetrate the aluminium bulkhead? What happens to the wireless signal when flying past airport radar or in the weather radar field of another aircraft?

Shielded wires are passive and relatively immune to electro-magnetic radiation, and are the means of choice for such a safety critical system.



Update

The OP was on fly-by-wire. In a sense, the flight control system is the most safety critical system on board and must be immediately available at all times. The presentation linked to by @mins in a comment reports on the progress of on-board wireless communication, for systems with a less critical safety aspect:


  Examples of Potential WAIC Applications 
  
  
  Low Data Rate, Interior Applications (LI): 
  
  
    
    Sensors: Cabin Pressure - Smoke Detection - Fuel Tank/Line – Proximity Temperature - EMI Incident Detection - Structural Health Monitoring - Humidity/Corrosion Detection
    Controls: Emergency Lighting - Cabin Functions 
    
  
  Low Data Rate, Outside Applications (LO):
  
  
    
    Sensors: Ice Detection - Landing Gear Position Feedback - Brake Temperature - Tire Pressure - Wheel Speed - Steering Feedback - Flight Controls Position Feedback - Door Sensors Engine Sensors - Structural Sensors
    
  
  High Data Rate, Interior Applications (HI):
  
  
    
    Sensors: Air Data - Engine Prognostic - Flight Deck/Cabin Crew
    Images/Video
    Comm.: Avionics Communications Bus - FADEC Aircraft Interface - Flight Deck/Cabin Crew Audio / Video (safety-related)
    
  
  High Data Rate, Outside Applications (HO):
  
  
    
    Sensors: Structural Health Monitoring
    Controls: Active Vibration Control
    
  
  




From the same presentation: An A380 has 5,700 kg of wires on board, and 30% of them are potential candidates for a wireless substitute. So wireless communication on board of aircraft does make sense, starting with the non-safety critical systems first.