SERVER-53150 changed hello/isMaster to not accept unknown parameters because all commands in API V1 are required to have 'strict: true' in IDL. However, we sometimes want drivers to advertise support for new features that old versions of the server don't know about via parameters in the hello/isMaster command. If we keep 'strict: true' with these commands, then older versions of the servers will fail to parse future requests since they don't recognize all of the parameters.
Since this ability to determine feature support has been useful in the past, it's worth preserving it. One way to do this would be to stop requiring that all commands in API V1 have 'strict: true' and change hello/isMaster to specify 'strict: false' in IDL.