I completely understand the purpose of creating a guild island : it's indeed a good way to encourage people to play PvP more often, and since PvP is (or at least looks like) the ultimate purpose of the game, it encourages everything else, including spending money on capsule coins in order to be able to buy good pokémons. I have nothing against that all, on the contrary, I think this is a very good idea.
However, the fact that only the 3 strongest guilds in the game can access the island has a drawback that can already be seen : people who are strong at PvP or who at least have a good Elo are changing guilds to secure their top 3 spot. What does it mean exactly ? Basically, we'll soon have 3 guilds with the best players on each server (and, most likely, the guilds will be the same in both servers) and the other guilds will have no chance to compete at all, and I really don't think it's a good thing. Basically, a few hours ago, in my guild (French Connexion), half of the players left to merge with another guild in order to make sure they would have the guild island. Is that what you wanted by making the guild island ? Well, if it was the case, then you did well. If it wasn't what you wanted to happen, there's a simple way to make things more balanced, and that's what I'll be suggesting :
Each month, in the previous month guildladder
1st guild would have access to the guild island for free
2nd guild would have to pay 1 million for the whole guild to access the island
3rd guild would have to pay 2 million
And so on. Number 10 guild would pay 9 million and the guilds that are not in the guild ladder would have to pay 10 million. It does make it more interesting to reach the top of the guildladder, however it doesn't prevent anybody to get it. The prices I mentioned are not as important as the idea of letting everyone go to it because, as you have already understood, people don't love their guild as much as they would love having access to the guild island.
I hope i made everything clear and, of course, if you agree or if you don't, I would be glad to hear any argument.