When I said mainstream, I literally meant mainstream. As in the "dominant" culture -- people who don't play videogames or only play a little. Perhaps the definition of that is the issue. The remake buzz and everything included in that Wikipedia article doesn't really speak to his popularity or recognition "mainstream". The reception section exclusively cites games media. So I continue to doubt his popularity in the "mainstream", at least in the United States.
Note: That doesn't mean he isn't a videogame icon, but he's not Pacman, PIkachu, Mario, or even Donkey Kong and Kirby. Unlike those characters, I doubt he would be recognizable to many outside of the gaming community. Regardless, he is one of the most recognizable characters they could have potentially added. Very few videogame characters are recognizable to "mainstream" audiences like those I mentioned earlier. It's still an explosive choice and the Final Fantasy series as a whole is one of the most notable in gaming. But none of that speaks to my comment, which is consistent with these beliefs.