Well, in terms of AEGS, Tokyo Marui are already doing it with some of the New Generation AEGs with the blowback and recoil already having metal exteriors. But on GBB pistols it's another question though many modern pistols now are actually not made of metal externally. Airsoftology talks about this in this Q&A episode:

"Tippmann Mail Call:

Another goodie arrives at the doorstep of Airsoftology and it's from RedWolf Airsoft. They sent over an RWA Fortis Switch 556 KeyMod rail for him to check out. This allows a tool less removal and can fit AEGs from Krytac and G&P, the PTW from Systema, and the Marui MWS GBBs as long as you get the PTS adapter. Find out how light it is in the video below.

Airsoftology continues with the visit to ICS Airsoft factory in Taiwan. In the first video of his visit, he mentions that the ICS CEO, Mr, Don Chu, lives on the penthouse of the ICS Airsoft building. Now he gets to sit down with him for this close-up interview... "Jonathan sits down with Mr Chu, the CEO of ICS Airsoft in Taiwan, to ask him 3 questions about the past, present and future of his company."

Airsoftology just answered on how to have the Taco pouches useful for SMG magazines in this latest episode of the Gear Guide... "If you own a MP7, MP5, UMP45 or any other Submachine gun, today's your lucky day... We're looking at the SMG's new best friend, the HSGI Extended Pistol Taco to see if it's the answer to your magazine retention prayers."