Firstly, I will say that yes, using the Append operation and manually managing your Index is a possibility within Couchbase and you could do it. But, it's important to remember that because of Couchbase' distributed Indexing and Querying engine, our Views in Couchbase are optimised to be as quick as possible.
Now; the Append operation, as you probably know is a non-JSON operation. It is also a very quick operation to perform. That said, if you are using Binary data, the Append operation cannot be used with JSON, as currently Couchbase Server can only concatenate two bytestreams. This means that it doesn't allow you to replace something within the JSON value.
I am also currently building a Scoring / Leaderboard example app for Couchbase, and the solution here, is to replace the whole document with a single operation utilising Couchbase' CAS value, for concurrency reasons.
However, if you are aware of this, and are using Binary data, the Append operation, as mentioned above is a very quick way of managing data.
Could you give me a little overview of your data structure? Are you thinking of using JSON, or non-JSON docs?
I hope this helps,