IMPALA-5120 the join strategy was changed from bcast to shuffle when tables have no stats. Adding a query option to specify the behavior lowers the risk that users may have come to rely on this behavior. This would allow them to revert back to the previous behavior.
Query option proposal:
Ideally, the default would be shuffle, but in the spirit of preserving existing behavior it will stay broadcast. We should re-evaluate this choice in a compatibility-breaking release.