Yes, but if it was opt-in...

Its nice if you can use groupcache as a memcache replacement even if some use-cases tie the hands of the implementation e.g. replication of hot items.

I've been thinking about something similar. I don't see how timed expiration would conflict with the two most important features - the filling mechanism and the replication of hot items. Am I missing something that would make timed expiration impossible?

Yeah on the first pass of the problem you seem right.

The CAS must have an authoritative node (my mind wanders thinking about replication and failover) but the key it protects - with the version baked in - can be replicated surely?