Center of the earth biom

It would be so cool if it were possible that you dig so deep that you can find some kind of world like the journey to the center of the earth movie. It could even involve new types of trees that don’t need sunlight to grow but they use glow stone to grow instead. You could  find all sorts of new things. I thought this could add another bison to the game and create more insensitive to mine. To get into the world you might also have to find a pare of giant wooden doors or something