Admin control to force "always in the cloud" ?

Thanks guys. 

With the new Files On Demand feature, it would be nice if an admin could configure the system to allow users to install the OneDrive sync agent but force it to set all files to "keep in the cloud" (or "free up space") for certain OneDrive or SharePoint libraries.

No need to allow users to install sync.  People are doing it today because we are rolling out the new engine a standard way for the next week.  We are allowing users to install right now as a way to jump the rollout line because there is so much excitement.

Admins have GP to turn Files On-Demand on by default for all their users.  Once the feature is on, all SharePoint libraries default to setting up as online-only (keep in the cloud).  If you have existing Sharepoint libraries there is also a policy to migrate pre-existing libraries to online-only.   To learn more read this article https://techcommunity.microsoft.com/t5/OneDrive-Blog/OneDrive-Files-On-Demand-For-The-Enterprise/ba-p/117234

So users could see all files via File Explorer, it would download them on demand when they need to read\edit something and then when they are finished, it would remove the local copy and just keep it in the cloud.

No, V1 is not automatically managing local storage.  This is definitely a direction we want to head in the future and our design accounts for it, but first we want to enable users to learn and understand the new model.  A classic example we worry about with auto cleanup is you double click to download it, it gets freed up some time later, and then the next day you want the file again and have to download it.  We want to make sure we are very thoughtful about this scenario.

This way the users have the familiar File Explorer interface but the owners of the company would rest easier knowing that all of their company data isn't synced all over the place on end-user devices.  

For V1 we don’t natively support this, but we intend to in the future.  We have enable tenants to do this to their own specification via scripting.  You can see how here https://techcommunity.microsoft.com/t5/OneDrive-Blog/OneDrive-Files-On-Demand-For-The-Enterprise/ba-p/117234

Is this currently possible or in the pipeline?

It is possible for tenants via scripting.  A policy control via OneDrive\Sharepoint is something we are thinking through, but don’t have a release timeline for.