Yea I love this idea. It would add more replayability and a few other games do this. Im gonna compare to terraria again. Relogic added a new biome variant to the corruption called the crimson in the 1.2 update. Each biome are now completely different which is very epic. Each of those evil biomes in terraria have different bosses, enemies, items, music, crafting recipes and alot more.
The binding of issac also does something like this where sometimes you can get the cellar floor or the basement floor, Or you can get the catacombs floor or caves floor. etc.
Now if we put this into dst image a variant to the dedicoius biome called the stone keep. So instead of a lush forest you would have the chance to get a stony place with stony npcs and stuff. So instead of pigmen you would get rocky people. Where they drop rocks when they get killed instead of pigskin and stuff. And there would be a stone king that gives you rocks instead of gold when you feed him meat. And there would be trees that drop stone instead of wood. AND bam we have a completely new biome in the game which is a 50/50 variant to the dedicous biome and you could get either one. So a playthrough that is dedicous biome would be completely different from a playthrough that is stone keep biome. And they can bring this idea even farther and add variants to the caves, ruins, savannah, lunar biome, pearl, and a lot more places aswell. The possibilities are endless.