many whoosh queries do not select on the namespace. as the namespace does not matter due to this, e.g. userprofiles namespace show up in the global items index.
some way to offer / select / switch namespaces (on the UI), the default should be NAMESPACE_DEFAULT (currently there is only one additional namespace (NAMESPACE_USERPROFILES), but there could be many more added by configuration).
be more selective in whoosh queries (include the current namespace similar to like we already select on the wikiname)
maybe we also need something like "search/operate in all namespaces"