bitcoin island is centralised and takes a large stake out of everyones pocket and puts it into one persons hands.
Not just one person's if the land is purchased by people pooling their money and voting using the blockchain toward what they want.
And the infrastructure can be created by others pooling their money toward different investments.
Billions are not needed for a small island with 20-30 land owners renting to visitors or selling out parcels.
20 people pledging 50 bitcoins each when the bitcoin price hits $10k then they have $10 million for the purchase.
That would be enough for this 36,000 acre island:
http://www.privateislandsonline.com/islands/ilha-das-pacas
A similar amount of 20 people pledging 50 bitcoins would be enough for a solar array with electricity sent to each of the 20 1,800 acre properties. Maybe even doing solar roads instead of a solar array to kill two birds with one stone.