Today's OS: CS6 will work, CS5.x is not available any more.
Future versions? No one knows it now.
But new functionality, like a working EPUB export you will never get with CS6. And you will fail in the exchange of data with service providers, agencies and others who will have to work with your files or from whom you will get files. For professionals it is not a good idea to avoid CC, as it is less expensive than previous buying versions. Additionally your get a lot additional stuff like professional fonts for no additional cost.