I would second this requirement. As the site grows, the use of the "merge communities" feature will most definitely increase...leaving us to maintain a laundry list of URLs. There may be some more requirements definition to be gathered around this...for example...what if a document is deleted or removed all together, how is that different than a community being moved...
Also, this goes into a previous post I had regarding the DocServlet. Any reason why doc resolution is converted to DOC-ID rather than communityId + Title? From the use-cases being presented to me from my end-users, I see resolution by name being the more dominant use-case. This is in regards to the UI changing Wiki links to DOC-ID if they are found.
These are great points...thanks for posting them..