How to beat the CAP theorem
OP adds confusion by calling data immutable.  Data has a well accepted common usage of being updatable.  Event is the term what OP wants.  Event is a snapshot of fact happened in time and cannot be changed and it's immutable.<p>What OP described in general is the append-log based approach to storing and querying data.  There are a whole bunch databases and file systems built on the append-log idea.  It's well worth the time to check out the research in this area to see the benefits and pitfalls of the approach.<p>Also check out the Complex Event Processing topic which bears similarity to what OP described.