While an individual may upgrade to Paratext 8 to become familiar with its features, the team project should not be migrated until the team is ready. It is possible for the administrator to do a test migration of the data, but then the project must be deleted from Paratext 8 and remigrated when the team is ready to switch.
We know that scheduling a time to migrate can be very difficult in places where teams are spread out in remote locations. To help, we have a working document on Deployment Strategy that talks about various team scenarios and how best to handle migration of their data.