There is definitely nothing that I am aware of done by us or partners. My guess is that even is subversion has a good API for getting content out, showing it in the standard Alfresco UI would involve quite a bit of work. It would be easier to do some sort import / synchronization than integrate subversion content into the UI.
I know for WCM, some customers use us as a source control tool, although Alfresco is obviously not as good as subversion for general coding tasks.