The Dark Knight Returns - if you were to do a sequel/prequel/spin off

This is something I've been thinking about a lot lately and I just wondered ignoring the Dark Knight Strikes Again and All Star Batman & Robin (which don't think even felt like the same world as the Dark Knight Returns_ if you were to write a prequel, sequel or a spin off what would it be (or even an animated version as a sequel or prequel to the animated films)?

I have to admit I'd love to find out what happened to Olivers arm, why are Superheroes banned, why does Superman only work for his country now? Did Lois die? Etc

Would just love to know what everyone has in their mind as a sequel, prequel or even a spin off?