Ideas for Flat World Presets

So, Flat World presets have been added to Bedrock. But there are many problems with the Flat World, and I'm wondering if they could be fixed. Firstly, only the Overworld is Flat. The Nether and the End aren't. Possibly, you can select a preset for each dimension, like for example having Redstone Ready in the Overworld and having a simple Flat in the Nether (using Netherack of course). Next, I'd like a 'Blank Slate' preset, where it's a layer of Bedrock at the bottom of the Overworld. For the Nether, you'd have one layer of Bedrock at the bottom and one layer at the roof. For the End, you could simply just have the Obsidian Spawn Platform that you arrive on in regular End. Nothing else would generate in the world, so it's perfect for custom map making. Also, why not have varying in biomes for Flat Worlds? You could keep it all flat, still, simply having the Grass colour change in different areas of the world. Finally, there is structures. It'd be ideal to be able to toggle on structures on a Flat World.