I recently convinced a client that they should use Office365 groups for this project we’re doing. The problem is that they already have a team site created, full of content. Is it possible to create an O365 group and tie it to an existing team site?
This is not possible at this point of time. But you could surface the data from the team site to the group site, using search webparts. You couls think of using Hub sites once they are available for you now. The rollout started couple of days back.