I don't see how CoinJoin can possibly ever be effective in a situation of address reuse.
Is Blockchain.info ever going to stop doing that?
I think they already have. Their default bitcoin transactions send change to new addresses, as does their CoinJoin.
I'm only using blockchain.info's coinjoin it to offload and split up my larger bitcoin purchases into cold storage. Hopefully it was sufficient enough for the last few deposits I made.