Sounds like capability security to me. Although I wish they had said more about how these namespaces work. If they are inheritable and you can virtualize them for child processes (as you can in Plan 9/Inferno) then I'd say it qualifies.
(Disclosure: I wrote the doc linked above.)
Yes. When creating the namespace for the child, the parent can map names to what whatever communication channels it chooses. If the parent wants to interpose on the child's access to "/dev/class/framebuffer", the parent could map that name to a channel that leads back to the parent.
> Can a process create a custom sandbox and run, say, AppMgr with limited permission to limit the permissions of all apps it manages?
Yes. That's useful for testing as well as for sandboxing.