The paradise island biome would be reminiscent of the long-gone paradise world theme in early Minecraft. It would spawn only as an island, similar to the mooshroom islands in that sense. Perhaps they could also be limited to a certain size, like around 10 chunks. The paradise island biome at its core would have sandy beaches, bright green grass in the center, decently flat terrain and no ravines or lava pools. Anything too dangerous would be excluded. Some special perks could also be applied to the biome, like perhaps causing a 1.1x speed up for crop growth, or a slight reduction in hostile mob spawns. This biome, also similar to the mooshroom islands, would be incredibly rare. (I don't know the probability of a mooshroom biome, but I would say just half or 2/3 that chance, and there is the paradise biome chance. This and the limited size would keep it from being too OP and exploited for farms or huge industrial districts.) If Mojang wanted to take this idea an extra step farther, a new tree type could be added, like the palm tree, which I'm sure has already been suggested a bazillion times. You could also increase a probability of nearby coral reefs or dolphin and turtle spawns, and potentially create an entirely new mob fitting for a tropical island. TL;DR ... The paradise island would condense the old paradise theme, nerf it a bit for game balance, and update the features to make it a perfect little slice of heaven in the regular old overworld.