Application developers generally use two APIs: a driver and the shell. As one of my readers points out, this makes API conformance between the drivers and the shell at least as important as conformance among drivers.
Let's implement the Driver CRUD API Spec in the shell: insertOne, insertMany, findOneAndDelete, etc. The old APIs can be deprecated, or not. The spec is written to avoid breaking backwards compatibility so existing mongo shell scripts and examples will keep working.