Microsoft has started to rolled out the guest access to Microsoft Planner.
This information was published to the Admin Portal with the following message:
We’re updating Microsoft Planner to support guest user access. We’ll begin rolling this feature out in the next few days.
This message is associated with Office 365 Roadmap ID: 14702.
Guest access in Office 365 Groups and Microsoft Teams enables end users to collaborate with people from outside your organization. If you decide to enable guest access, as administrator, you can grant access to group conversations, team chats, files, calendar invitations, and the group notebook. With this update, guest users will also be able to access Planner plans for any groups and teams they’ve been added to.We will begin rolling this feature out over the next few days, and we anticipate rollout completion by the end of April.