Furthermore, there are some capabilities in SharePoint, like a modern page, that can be turned on and off on a user by user basis. Many of these use client side rendering and are good candidates for features that can be deplyed early using First Release People. However, there are other parts of the service that require service-level configuration, and the back-end configuration for process-to-process communication and security requires that all users in the tenant are enabled for this feature for it to be effective. We continue to refine the ways we can provide early access to code and features for testing as flexibly as possible, so we'd encourage you to consider either First Release tenantwide, or getting a trail tenant for testing that can be used in First Release Tenant mode.
