I might add, that 'Sibling' connections should only be automatically established between spaces with the same administrator.  Sibling connections between spaces with different administrators, should probably be handled as a request that must be accepted before the connection is finalized(Just because someone wants to call you a Sibling, doesn't mean you want to be one)  Siblings with different administrators, must of course, be able to break the connection at any time.

This does add a degree of complexity to lateral relationships.  It would be nice to have some day if feasible, but by no means anything urgent.