It may have been suggested before but if not then i'd like to suggest a guild based world quest, it would bring a competiveness to the game that pvp doesnt as not every guild in the game is pvp orientated and maybe 4/5 guilds out of 20 on the guildladder have a real chance of entering guild island.
I think the game is missing a trick here with the lack of PvE content guilds can collectively compete in.
Rewards for winning the world quest could be guild pokeballs with the catch rate of an ultra ball and guild island for that season.
etc