Airsoft MILSIM across the globe is seeing a shift in players getting away from HICAPs because of the unrealistic winding, granted in the old days, winding took (in theory) the same time as reloading a real mag, but in simulation sense you cannot carry that much ammo in real life (my Battalion carried 14 magazines, a total of 420 rounds of 5.56mm), and most MILSIM airsofters apply the 10 BBs to every 1 real round, 30 real rounds equals 300 BBs for airsoft, which justifies the use of HICAPS, it still might take away from the realism factor.
Kal also pointed out another fact, GBB rifles still suffer from outdoor weather effects, too cold or hot and the weapon could become unreliable. Plus sustained firing also effects the weapon.
Electric blowback, now that is becoming more and more viable.