Given that we can drop the hashed index, it means we also don't have to require it in the first place when someone is sharding a collection with a hashed shard key.

Today, people have to build the hashed index, shard the collection, then drop the hashed index. Building an extra index not only takes time, but also impacts your workload, both the index building itself and the existence of an extra index even if temporary.

So let's not require it in the first place for hashed shard keys.