mongorestore, mongoimport should have an option to bypass document validation (validation will be on by default).
This is meant to be in alignment with other places where we allow pre-existing data to be out of conformance with the validator. mongorestore is arguably dealing with pre-existing data and used for backup/restore purposes. Without this bypass, that use case is no longer available.
This may require an upgrade of the mgo driver to allow the insert write command to support this option. See: https://docs.mongodb.org/manual/release-notes/3.2/#bypass-validation