1.17 biome blending

When you update a Minecraft world, a lot of the times your get ugly straight borders between biomes when you explore farther. I am really worried about this for 1.17. I really want the new blocks in one of my worlds, but I don't want to ruin the terrain, especially if the sea level is going to be raised. We need a way so that the biomes can blend better. I also think that we need a feature, that if the sea level does change, that it won't just create a huge hole. This update has the capability to destroy worlds, and halt them from updating again. I don't want to live a big hole, or there being a huge wall blocking us in. I hope there is a way to make everything built to get moved up however many blocks the ocean did. I'm sure I'm not the only one worried about this.