Hope this is the right spot, but this is a feature we could use a lot and I imagine others could too.
Team folders/groups give nice powerful admin control features, but you currently cannot add a 3rd party or parties to a group or team folder, only people who are under your paid account. In our industry (construction) we have a lot of joint venture projects among multiple companies, and each company already operates and pays for their own dropbox business account. The issue is that we need a shared collaborative storage space, but a typical shared folder does not off the level of admin control that a team folder does.
The request would be to all admins to add users of other dropbox accounts to a team or group (provided they accept the invite) so that users across companies working on the same project can operate in the same team folder with all the controls that come with that. We are currently on a large 2-company and another large 3-company project, and all 5 companies run their own paid dropbox business accounts. The only way we can share on the projects is to use a shared folder, but it would be great if the managing company of each project could just create a group for that project and then invite employees of the other company to join that group and thus then be given access to the team folder for Project #1, Project #2, etc.