One possible solution I see for the Tag Divergence problem is errors. When people communicate verbally, mistakes are often made and miscommunication results. What if such miscommunication is possible in a tag system? What if services like Flickr or Delicious are capable of confusion? This idea sounds crazy at first which is a good sign. 😉
Let's see. What if similar tags (in terms of edit distance or some other aspect) were merged randomly? Tags like dog, dogs, dag, and dig would get confused (aka merged) into one. It doesn't matter which tag is chosen because more common tag will eventually emerge. Problems stemmng from intentional tag confusion mechanism needs to be minimized but I don't think they are serious if they are constrained appropriately.
Accumulation of confusion over time has a kick on it's own so I think confusions have to be soft. I am still trying to figure out what soft means so don't feel bad if you don't understand what I am saying.