This is a weird situation but there are times when we have different development teams working on our projects (either multiple different outsourced team or an outsourced team paired with internal developers). Since this is a tricky situation, we would love to separate the work being done by the different parties so that they are not visible to what others are working on but still have the issues/items coming from a universal backlog. The easiest way to implement this would be to have multiple boards on a project but I do not think you can change permissions and restrictions on boards...unless I am incorrect. This is why I am wondering if you can create a parent-child link between projects, or some sort of connection, where the backlog items will act as one but I can have different restricted boards for different teams.