The whole car is already in ground effect, and moving to venturi tunnels would just change the nature of the problem. Short of complete aerodynamic standardization, there's no aerodynamic solution to overtaking.
As an aero package is developed, efficiency becomes increasingly reliant upon complex interactions that are more and more sensitive to turbulence. This is true of any concept you can imagine, and it means cars in advanced stages of development will tend to be more sensitive to "dirty air." It's why Hamilton had great difficulty following Vettel at this year's Spanish GP...
(It's also why IndyCar's problems with "dirty air" are practically non-existent when compared to F1.)
Overtaking is about performance differentiation, and trailing cars will always have worse aerodynamic efficiency. Think of it this way: running is another car's wake is like temporarily reverting to an older-spec car. Even fan cars would be susceptible to the problem, because the better designs would inevitably feature aero advantages that exist outside the influence of the fans, which means the better cars would still be more sensitive to turbulence.
As a problem without a solution, I think it's best to just accept it and move on to something else.