See some discussion in D13156.
Having built enough of Spaces to click around them a bit, giving spaces very hard boundaries (where you can either see the space and stuff inside it or you can't) feels like the right way forward, and softening boundaries to support the "Security" use case doesn't feel great (it adds a lot of complexity to configuring and understanding spaces).
However, the security use case is a mandatory use case for WMF and their interest in Spaces.
An alternative to softening the boundaries of Spaces is pushing Nuance up and giving it enough capabilities to supporting a dedicated security queue. This is preferable in a lot of ways. In particular, it would let you keep the reporter in the loop without sharing everything with them.
It's undesirable in that it may be a lot of work.
I'm going to look in to how practical this approach might be, so we can evaluate it against softening the boundaries of Spaces or making them act after automatic capabilities.