I think it would be really cool to be able to rename a column, or, more generally, a move command to move data from one column to another in the same CF without the client having to read and resend the column value.  This would be extremely powerful, imo.  I suspect the execution would be quick and could even be made atomic (per node) as I suspect it would mostly entail only reference updates.  Has anything like this been discussed before?  Seems like such a natural operation for a hash-table-like data store.