Building on animals?

We have animals that we can Farm, tame and ride why not have mods that we can build on like a house. Let say there a big turtle that we can build on his back and be able to go under water and still me in your house cooking meat or have a longneck on land where we can build a home on, you would be able to control the mod like your riding a horse but then you aren’t riding it just on it’s back in your home it’s walking around roaming. I think it would be amazing idea where we could build on a mod it brings a new aspect in Minecraft a new type of mod for the future of Minecraft.