I understand that a current CC Lightroom catalog will never be backward compatible with a old version like CS4 stand-alone Lightroom.
But if at the end of my year Cloud subscription, say in August 2015, will that cloud's version be compatible with the current (at that time) standalone version?
Example, Cloud Lightroom might be at Version 5.5 (or whatever) and the Stand-alone version might only be at 5.0 - would I then have compatibility from 5.5 backward to 5.0?
Or put another way - will Adobe in the forseeable future allow same version backward compatibility from the Cloud to the Standalone?
As things are right now, yes you have compatibility. In fact, you would be able to update your standalone version to Lightroom 5.5. You would have exactly the same program version that you had in the creative cloud. However, if Lightroom 6 is released and you are using it from the creative cloud, then it would be necessary for you to upgrade your standalone version to Lightroom 6 in order to continue using your current catalog. That's assuming, of course, that Lightroom 6 will still be available as a standalone program. The unofficial word that I have seen is that it will still be available.