I just realized CoinJoin is actually an effective scaling tool; no longer would we have to increase the block size to handle more tx/s. Just bundle them in CoinJoin txs.
It could be used as a load balancing device for a system with a fixed block size limit. CoinJoins happen automatically to help compress more transactions into the available block space. This could provide a good argument against a scheme with a continuously variable block size, or to a scheme with no limit at all (although I don't think anyone has yet made any serious proposal for the latter)
It also illustrates that CoinJoin really is just that, joining inputs and outputs into single transactions, regardless of the utility you're seeking from doing so.