Hey,
reading your point 1 I think you misunderstood. I was comparing the internal work needed to fulfill requests needed for a queue-concept. The quoted CBQueue implementation works in a multi process environment already and has a very low overhead as only pre-optimized CB structures are used (thats what I was talking about with hashes and B+ Tree; see http://developer.couchbase.com/documentation/server/current/architecture/storage-architecture.html).
The Sub-Document commands are nice but as far as i can tell not optimal for this use-case. The goal here is to minimize network traffic by sacrificing some cpu usage on sub-doc searches. Direct key access to the needed information will still outperform those lookups. Sub-document commands are designed to save on large-document updates/queries but avoiding large docs if possible will still be better.