To help integration with other tools, you can now direct Reviewable to sync its pending reviewers to GitHub's requested reviewers in the Publish options dropdown:
This tries to keep the list of requested reviewers updated with the latest people who need to take action on the review (within GitHub's constraints, at least: collaborators only, no PR author). Super useful if you've set up something like Pull Reminders to ping you about pending reviews on Slack!
Docs here and exact algorithm here. As always please let me know if you see breakage.