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.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.Also check out the Complex Event Processing topic which bears similarity to what OP described.