Has anyone tested or flown permeable wings to increase efficiency?
Not really a great answer but:
Tested - yes I believe so.  Actively used - not to my knowledge/unsure.  The structural complexity of this is challenging, and the cost to benefit probably isn't compelling enough for &quot;traditional&quot; configuration aircraft.
You may find this of interest A History of Suction-Type Laminar-Flow Control with Emphasis on Flight Research or Aerodynamics of Permeable Membrane Wings