Oh! The link! Um...not really it's the basics for becoming a GS for any of the Aeria games.
But you are correct that the GameSages guild is GMs and GSs only, because it makes it easier for players to identify who is a GS since there is no GS border around our avatar.
However we do not let people become GS any time there are times when the team will be accepting applicants, so until then following the How To Guide is a good way to make sure you've fulfill the requirements and make yourself stand out from other candidates.