I am not sure that I understand fully what you are trying to get at. When you mention private IPs am I correct that you are talking about the RFC1918 addresses (10.0.0.0, 172.16.0.0, and 192.168.0.0)? It is certainly possible and proper to route these addresses within your own network. It is problematic trying to route these outside of your own network. If you send routing updates outside of your own network you should not be advertising these networks to other public networks.
I am not sure about the last part of your question where it talks about using NAT to get to the Internet. I have a customer who has a class B address space which they use on their internal network. They do NAT all of their traffic going to the Internet. I think that is entirely proper.
If these do not address your question adequately then perhaps you can clarify your question for us.
We are pleased to announce availability of Beta software for 16.6.3. 16.6.3 will be the second rebuild on the 16.6 release train targeted towards Catalyst 9500/9400/9300/3850/3650 switching platforms. We are looking for early feedback from custome...