setting numshards dynamically for TextIO.write()

I go through code for TextIO. It uses WriteFiles  in TypedWrite. Now, WriteFiles has the functionality withNumShards(ValueProvider<java.lang.Integer>) and withSharding([PTransform|https://beam.apache.org/releases/javadoc/2.9.0/org/apache/beam/sdk/transforms/PTransform.html]<PCollection<UserT>,PCollectionView<java.lang.Integer>> sharding) but TextIO or its inner class TypedWrite doesn't have that. It would really be a great to expose that functionality to user.

Are there some issues in implementation that this is not already available?