It is unsafe to perform check on feature flags that are bounded by FCV on the router. We will need the check to the primary shard. The new workflow will be:

• Route the createDatabase command always to the primary shard
• Check if the feature flag is enabled
  • If not, send the command back to the config server to execute the old code path
  • Otherwise, continue executing the new path

We might be able to take advantage of the primaryShard option to avoid rerunning the primary shard selection on the config server.