1. I'm not aware of any plans to backport this.
2. Again, I don't know of a way to list subpartition the table. But you can change the partition interval with:
DBMS_AUDIT_MGMT.ALTER_PARTITION_INTERVAL(
interval_number => 2,
interval_frequency => 'MONTH');
This will create a partition every N intervals. So the above is one every two months. You could change to daily with:
DBMS_AUDIT_MGMT.ALTER_PARTITION_INTERVAL(
interval_number => 1,
interval_frequency => 'DAY');