However, I also believe that modern RC paper base is a lot more permanent than earlier ones. I also agree that antioxidants added to the polyethylene resin are not usable in baryta sizing layer. Those antioxidants have to be nondiffusible but there is no good way to make hydrophilic nondiffusible antioxidants to add to baryta sizing, but it's easy to make nondiffusing hydrophobic antioxidants for polyethylene.
Another consideration is that I have a final rinse solution that adds UV blocker and antioxidants to the print. (Similar idea to sunscreen protection but with extra antioxidants.) I'm not sure why Kodak or Fuji never came up with this kind of solution (perhaps cost consideration, as the ingredients are not very cheap), but this treatment is very effective with untoned silver images on RC base in my testing with UV and oxidizing agents.