Right, but that's not relevant for 1:1 NAT (well, at least it doesn't have to be). Since the NAT would happen in software, you're no longer constrained by subne

Right, but that's not relevant for 1:1 NAT (well, at least it doesn't have to be). Since the NAT would happen in software, you're no longer constrained by subnets being physically under routers. 11.2.3.0/24 could contain 10.0.1.0/24 and 10.128.128.0/24 without any issues, assuming they don't use in total more than 256 address.