Adding a limit in guild size sounds like a good idea. It might be better if the guildmaster itself be the one to add a guild cap (like an additional feature that only the gm can execute where he/she can set the guild cap to a particular number or disable it if he/she don’t want to add a limit). Again, players are free to choose what guild they want to join for as long as they meet the requirements of the guild that they will be joining and the guild itself can accommodate and is pleased to have them.