Along with Deployment plan or flow restrictions, it would help the complete automation if there is an option to setup Approval process. This way we don't have to maintain separate email chain for tracking the approvals for Production release.

To expand on this, it would be ideal to setup your Connections, then create a "Deployment Plan/Workflow" where you predefine the flow of metadata from org to org. Maybe provide a UI that allows you to click and drag Orgs onto a sheet and create a flow chart? This would help everyone visualize how metadata moves if there are multiple build, UAT and staging environments. You could also tie in CI operations and monitoring capabilities to really paint a picture of the health of an org and it's supportive structure

Once this functionality is built it could be called "Deployment-Diodes"!

di·ode
/ˈdīˌōd/

a semiconductor device with two terminals, typically allowing the flow of current in one direction only.

To build on the comments, it would be great to not only prevent deployments to production, but also have the ability to enforce a deployment up a stack, so that deployments can not skip environments. For example, enforce that Developer Sandboxes can only deploy to a Dev org, and a QA org will only accept deployments from the Dev Org and Prod will only accept deploys from QA.

When using Change Sets in Salesforce, native functionality requires a Deployment Connection between two SF orgs to send changes from one org to another. There is currently no limitation within Gearset that would limit which org can deploy to another org if a user has logins to both orgs. It would be ideal if Gearset had this functionality/this feature so deployments are limited to the appropriate orgs.
https://help.salesforce.com/articleView?id=changesets_about_connection.htm&type=5