These are the things I thought:
1- Leveling system. Guilds start lvl 01 and can reach other levels based on Guild XP 2- A min number of players to create the guild (like 5) and a maximum that can be extended based on guild level 3- Guild XP gained through the completion of daily missions by its members 4- Guild members ranks - Leader, officers and so on 5- Property license for Guildhouses 6- Special Guild Respawn Waypoint linked to town 7- Guild permissions based on guild member rank or nominal, so that common areas and exclusive areas can be created inside the guildhouse 8- Equipments inside Guildhouses could become more efficient based on Guild level (faster production, more room for items, better success rate, quality boost and/or greater output) 9- Seasonal events envolving guilds, like guild wars 10- NPC in town for guild-related questions
I think these wouldn't take much coding to create. I hope those ideas help!
Allbart - Andromeda