Ephemeral buckets are, and have always been available in CE for core Key-Value operations, however certain additional functionality such as XDCR and Secondary Indexing are EE-only features.
I did note that https://www.couchbase.com/products/editions isn’t clear on this - it marks Ephemeral as ‘X’ for CE when it really should highlight there’s just a subset of features in CE. I’ll raise a doc bug on this to get it clarified.
Couchbase Server 6.0 certainly wasn’t make explicitly more CPU intensive!, However it could be that some of the additional new features use more CPU than previously. Certainly for the Data-Service, if you are using the same feature-set between 5.x and 6.x I wouldn’t expect to see an increase in CPU; if anything you might see a reduction.