When creating an External Table, it'd be awesome to have the option of NOT allowing writes to it (disallow any INSERTs or if hive ever allows UPDATEs). Adding and Dropping Partitions should still be allowed.
This will enable hive to "play well" with external data stores other than hdfs where data should be non-maleable.
I'd recomend the following syntax, which applies ONLY to external tables:
CREATE EXTERNAL [READONLY] TABLE ...