All the above being said, I need to point out the following...
We introduced a new feature early this year that some of you seem not to have noticed. Within the automatic link detection dialog, every presented option shows its entire containment tree beneath it. In other words, for all practical purposes, every offered match shows you its "namespace". While this isn't perfect, and it still requires you to choose an item from the list instead of magically divining the particular "namespace" you happen to want at a given time, it's still PRETTY DARN CONVENIENT.
One other thing to consider. We introduced the concept of the "master scoping filter" a couple years ago (or more). The thinking was that it would provide the rough equivalent of namespaces. It allows the user to effectively define his own namespaces via tagging and then employ those namespaces at will. We even restricted automatic link detection to it at one point to give exactly what is being asked for above. Nobody used it. It seems nobody liked it, despite the versatility it provided. So it's quietly fallen off into a neglected corner, although it's still there for anyone who wants to play around with it. I think the official name is now "global filter", but it still behaves the same way it always has, except it no longer constrains automatic link detection. Feel free to check it out.