SteveHowell contributed a LocalSiteMap feature to MoinMoin. One of the other Python wiki implementations may have it.
Is this really an IndexingScheme? It is just a visualization of the place you are already at, rather than a different topology that makes connections to different places elsewhere in the graph.
Sure, why not. Let's not get Aristotelian.
See TouchGraphWikiBrowser, HowDoesThisWikiLook