There are some use cases where a data model is shared between multiple keyspaces. It would be useful to allow applications to reuse the same mapping configuration and the same C# class to map to multiple keyspaces (and maybe tables?).
Example use cases:
Two similar tables on separate keyspaces due to multiple RF requirements
Two similar tables on the same keyspace due to multiple partition key requirements
For reference, here's how the java driver 4.x solves this problem: